All SF characters

According to my count, there are 77 total characters that have appeared in a Street Fighter game (as a playable character) so far.  This is, needless to day, a lot of characters, and even if you look at titles like Ultra Street Fighter IV that have well over 40 playable characters, barely passes up the halfway mark.  Let's go through them very quickly alphabetically and I'll give some brief background on each.

• Abel a Frenchish judo fighter that appears so far only in Street Fighter IV, Abel's story is that he was a body intended for Bison's use; a kind of male doll program, except cloned rather than kidnapped.  For whatever reason, he went rogue and sentient and became Abel.
• Abigail I have no idea why Abigail is a man, but he was originally one of the later appearing bosses in Final Fight, and was added as a Season 2 download to Street Fighter V.  He's absolutely huge; bigger even than Hugo, and reminds me of the Marvel mutant character Strong Guy.  He's also a pretty stereotypical dumb jock
• Adon Originally the next to last boss in the original Street Fighter, Adon was Sagat's pupil.  He later appeared in the Alpha series and Street Fighter IV, now rebelling against Sagat, and being a general nuisance.
• Akuma Originally appearing as a super secret character in the last version of Street Fighter 2, Akuma has become one of the most popular characters, and has appeared in just about every Capcom fighter since then.  He's meant to be the dark mirror image of Ryu's old master, and a rival to Ryu himself—he eventually grew to become one of the most iconic villains of the series.
• Alex Originally meant to be the protagonist of the ill-fated Street Fighter III, Alex did finally come back in Street Fighter V.  He's a kind of rock-headed wrestler type with really strange, gay suspenders and stuff.  He struggles to find a place as a protagonist because he's not a very interesting character from a moves, personality, or plot perspective.
• Balrog Discounting the name-swaps between the US and Japanese versions of the game, Balrog was based on Mike Tyson, and was the first boss of the SF2 game.  He's appeared in the Alpha, IV and V games as well.
• Birdie originally a character from the first Street Fighter, Birdie was revived for the Alpha series, and then later for V, getting progressively sillier as time goes on, for whatever reason.  
• Blanka one of the original (and weirdest) of the World Warriors from SF2, Blanka has appeared in every series since except III.  His connection to the rest of the cast is rather tenuous, so they've tried to imply that he was friends with Dan, and Sakura and others.
• Cammy originally an agent type with amnesia who was supposed to have been Bison's lover, Cammy later developed a much more complicated backstory as the lead doll agent from Shadaloo.  She appeared in an update to SF2, and has been in every game series (except III again) ever since, and has become one of the more recognizable characters from the series, as well as having more plot importance than most.
• Charlie (Nash) originally merely a backstory element to Guile, Charlie (also called Nash; later determined that his full name was Charlie Nash) appeared in the Alpha series, and then as a weird Frankenstein character "rebuilt" and resurrected by Shadaloo in SF V.
• Chun-Li Chun-Li is one of the few characters to have appeared in III from the earlier series, and is an original SF2 World Warrior.  Ironically, her plot importance has often faded over time.
• Cody one of the main protagonists of the Final Fight series, he was brought into Alpha—how as a psychotic convict imprisoned for being unable to ever stop fighting.  He appeared again in IV.  He has no plot importance beyond Final Fight, but is tied to a great many characters in the game.
• Crimson Viper a IV and V character; one of the few that seems to not be ridiculous.  She's a secret agent with a battle suit that gives her super powers, making her a similar concept to Black Widow—although for some odd reason, it was decided that secret agents in SFverse can be 20 year old single mothers (!?)  She's undercover, pretending to work with S.I.N. but really serving the CIA.
• Dan the infamous joke character that riffs off of Robert and especially Ryo by SNK in Art of Fighting.  He appeared in Alpha, IV and there are brief references to him (although no actual appearance) in V.  
• Decapre a IV representation of the doll agents.  In this sense, she kind of replaces Juli and Juni from the Alpha series.
• Dee Jay a late appearing SF2 expansion character, who also appears in Alpha and IV.  Like many of the original World Warriors, he actually has surprisingly little plot importance; I suspect that that is something that was developed later, and new characters were developed often with a plot imperative behind them; while other characters already existing, Capcom didn't quite know what to do with.
• Dhalsim an original World Warrior who appears in every series except III.  He often plays a Yoda like mentor role, but originally he was just supposed to be a colorful Indian rubber man archetype
• Dudley the British posh boxer who first appeared in III and later became popular enough to migrate to IV as well.  He's supposedly Balrog's rival and antipode
• E. Honda an original World Warrior that's appeared also in Alpha and IV.  Like many ancillary World Warriors, his plot importance is negligible
• Eagle originally a SF 1 character who was revived as a sprite for a spin-off title, and was later added to a handheld version of the final Alpha game.  There's not much to tell about him, really.
• Ed appearing in a IV ending, he was later brought forward as a V expansion character, and another Shadaloo cloning experiment gone somewhat awry.  As a boxer of sorts, he's been one of the few characters tied to Balrog.
• El Fuerte this guy's a loon, from IV.  He's too crazy to have caught on with anyone, really
• Elena a strange, "cute" character from III that was also in IV.  She has a weird "Storm" (from the X-men) vibe, but for some unexplainable reason, fights in a Brazilian style.  She's relatively non-serious, and Capcom has even joked that she became friends with Akuma.  Probably to establish clearly the fact that she's a silly character, not to be taken seriously.
• Evil Ryu technically, this is an alternate character; a "dream" character, not a real one; a what-if.  Appearing in Alpha, then IV, Evil Ryu has undergone a fair bit of development to his moves and appearance over time, to the point where he much more resembles an original character.  Technically, however, he's not.
• F.A.N.G. a V character, designed to be one of the sub-bosses (and therefore important to the plot, and one who appears a lot), but he's pretty silly.  I'm trying to think of what Hong Kong action movies he's clearly drawn from, and his poison abilities are kind of unique.  He's really too stupid and caricaturish for my taste, though.
• Fei Long an expansion character from SF2 that is obviously the ersatz Bruce Lee.  He's appeared in Alpha, IV makes a brief cameo in V.  There have been some half-hearted efforts to tie Fei Long to more characters, but he's still ancillary to the plots of the games.
• Geki a claw-wielding, star-throwing, and teleporting ninja from the very first game, who represents the then-current supernatural ninja craze.  He never appeared in any other game since, although there are hints that 1) Vega is a protege of some sort, and 2) a Geki II character may be in the works.
• Gen one of the few SF1 antagonists who got a fair bit of development, appearing in Alpha and IV, and being made out as fairly significant in the backstories of several characters, including Akuma himself.  In fact, he makes a brief cameo appearance in Akuma's story, where its implied that he finally dies for real.
• Gill the boss of III, and therefore largely unconnected to anything else—although as V starts to take the 2, Alpha and IV stories and lead them to III, characters that relate to him and his organization start to take more shape.
• Gouken although he's supposed to have been dead all along, Gouken was brought back as a playable character in SF4 and makes a cameo in V.  He's Ryu and Ken's master, and Akuma's brother.
• Guile an original World Warrior, who's been in every game except III (although he was a late appearing expansion for Alpha, where Charlie was supposed to have replaced him) who has been made significantly important in the Shadaloo story.
• Guy an alternate protagonist from Final Fight who's also been in Alpha, IV, and in cameo form in V.  Like Geki, he's a stereotypical 80s/90s supernatural ninja, except the good guy version.
• Hakan a IV character who's another rather silly one.  Partly because of this, he's been somewhat tied to some of the other sillier characters, like E. Honda.  He's also meant to be about as exotic as Blanka or Dhalsim... which he is.
• Hugo (Andore) although under a slightly different name, Hugo is actually a Final Fight character who was ported into III and then appeared later in IV.  Until the appearance of Abigail, he was by far the largest SF character, and is quite dumb.
• Ibuki a teenaged girl ninja; a weird Japanese cultural affectation.  She appeared in III and then IV and V because she was relatively popular.  She's got a little bit of that Spider-man "fighting crime incognito while also dealing with school" vibe to her, but honestly, I've also found her too culturally Japanese to really get.
• Ingrid a character from another game who was thrown into the final, handheld version of Alpha 3, because she could be, Ingrid has no ties to anyone else in SFverse, and is kinda weird.  She's actually got a strange anime and/or SNK vibe to her in my opinion.
• Joe a completely forgettable fighter who only ever appeared in SF1.
• Juli one of the dolls, made playable briefly in the final version of Alpha.  I'm considering all of the other Dolls as background characters, even though some of them can be fought as antagonists in SFV.
• Juni same as Juli; although her sprites and moves are slightly different
• Juri a villainous character from IV and V—one of the few IV characters who, like C. Vyper, is memorable enough to have moved on
• Karin an Alpha 3 character who later becomes an important plot character in V.  At first, she's just a throwaway rival to Sakura, but she later becomes more like a more serious female analog to Ken.  Not in terms of moves, just in terms of plot positioning.
• Ken the very second SF character ever developed; originally a red-clothed, American copy of Ryu, but one who later developed his own personality, moves and style.  Sometimes he's treated seriously, but occasionally he veers into silliness (his Roy Rogers alternate costume in IV, for instance, or his III story)
• Kolin a V only character; an undercover agent for Gill
• Laura supposedly the sister of Sean, this V only character plays more like Elena
• Lee a completely forgettable 1 only appearance.  He's been retroactively tied—tenuously—to some other Chinese characters, like Yun, Yang and Chun-Li
• M. Bison the boss of SF2, and a character in every single game since except III.  He's still the most iconic SF villain, and replacing him with the strange Gill for III was probably part of it's failure to grab the audience
• Maki a Final Fight character who only appears in the hand-held Alpha 3 game, she's quite tall for a lady, and has ties to Guy and Cody and some of the other Final Fight guys.  
• Makoto a III character who later appeared also in IV.  She has, like many III characters, no connection to anyone else, and appears to be (although this is officially unconfirmed) to have been inspired by the Akane Tendo character from Ranma ½.
• Menat the very newest (so far) V character, she is an apprentice to Rose and has an Egyptian vibe to her (including an alternate costume where she's wrapped like a mummy.)  Just in case you thought what Rose needed was a cute, teenaged apprentice girl.  
• Mike a forgettable SF1 character who may have been a prototype version of Balrog, although Capcom tries to say, no, there's just two characters built on the exact same archetype.
• Necalli a strange V only Aztec demon-god character, who has a Darkstalkers vibe to him, or something.  He could have been developed as a peer, if you will, of Akuma, but Capcom didn't really seem to know what to do with him from a storytelling perspective
• Necro a III character (with a cameo in V) who looks very bizarre, likes to sing opera in falsetto when he wins, and has Dhalsim's Indian rubber man stretchiness as well as Blanka's electricity.  He's supposed to be a runaway experiment of the Illuminati, although why both the Illuminati and Shadaloo were so caught up in cloning/superhero experimentation I don't know.  It does tend to make both organizations run together.
• Oni this is a dream version of Akuma in the same way that Evil Ryu is a dream version of Ryu.  From IV only
• Oro a very strange III only character; an ancient man who wants to date Ibuki, and he looks about as freaky as Blanka or Dhalsim.
• Poison another Final Fight character who finally became playable in IV.  She's also cameoing along with Hugo in III.  There were some weird ideas floating around for a while that Poison might have been a cross dresser or even a post-op fake woman.  
• Q a completely mysterious III only character, about which we know very little except that he looks like the Invisible Man
• R. Mika a rather dumb expansion Alpha and V character who is a groupie to Zangief.  She's one of the silliest characters (non-III) in the series
• Rashid a swashbuckling V character who has been made out to be a semi-protagonist of that game
• Remy one of the latest appearing III characters; a skinny, androgynous, emo Guile clone.  Blegh.  He belongs in a King of Fighters game
• Retsu a disposable Japanese monk character from SF1
• Rolento originally a boss in Final Fight, Rolento has since appeared in the Alpha and IV games.  Like many Final Fight characters, he really only connects plotwise to other Final Fight characters.
• Rose an Alpha and IV character who has strange ties to Bison.  Unlike many of the female characters, she actually appears to be mature and composed rather than "cute" and kind of spastic.
• Rufus another one of the undeniably stupidest characters in the game, Rufus is a IV only character who supposedly has a rivalry with Ken.  He's loosely based on Chris Farley's Beverly Hills Ninja, but dressed like a basketball stuck in Bruce Lee's Game of Death outfit.
• Ryu the protagonist of the game and series, the mascot for Capcom overall (along with, maybe, Megaman) and one of the few characters (only Ken joins him here) to appear in every single SF series.
• Sagat the boss of SF1, the sub boss of SF2, and a powerful figure in every SF game except III, and (curiously) V, where he is supposedly kind of retired.  He has evolved over time from being an outright villain into being more of a respectful rival to Ryu.
• Sakura a popular Alpha creation who also appears in IV and V (as cameo); Sakura is a "cute" teenaged girl who idolizes and copies Ryu.
• Sean Ken's apprentice from III; an otherwise completely forgettable character who plays to Ken in some ways the same way Sakura does to Ryu
• Seth the boss of IV; a Bison clone who went rogue and became significantly inhuman
• Shin Akuma a "dream" version of Akuma; supposedly Akuma not holding himself back.  In this, he differs from Oni, which is a future-state version of Akuma.  He appears in the Alpha games, the version of Akuma from SSF2 Turbo was retroactively called Shin Akuma, and he's a secret boss in one of the of the III games.
• Sodom (Katana) another Final Fight boss that appeared in Alpha, and has (so far) never been moved from there.  He's weird; an American obsessed with Japan, or something like that.  Not very memorable.
• T. Hawk a SF2 expansion character who also appears in Alpha, IV and has an interesting story tie to Bison and the Dolls, actually.
• Twelve another dumb experiment from SF3; Twelve has no personality; no nothing.  He's a shapeshifting android or something that can copy the moves of other characters
• Urien Gill's more human-like brother, a resentfull sub boss type character.  While he was kind of a stupid foil in III, he's been made a more serious and significant villain in V
• Vega the spanish "ninja" sub boss from SF2, who's been in every series since (technically, he hasn't "appeared" in V yet, but his upcoming presence was already confirmed.)  As such, he's got a lot of story ties to a lot of characters, including all of the Shadaloo ones, and Chun-Li especially. Ties to Cammy and Juri have been invented as well.
• Yang a popular Chinese teenager from III who has been brought into IV.  Other than ties to his twin brother Yun, he seems to also know Chun-Li (because everyone from China knows each other or something) and otherwise has few ties to the storyline at all.
• Yun see Yang above
• Zangief an original SF2 world warrior who continues to appear in the game, but has devolved into silly comic relief.  It's curious that most of the world warriors, who were seen as antagonists if not actual villains at first, have gradually become supporting protagonists and "heroes"—at least if the SF5 story is any guide.  In spite of this, Zangief's probably biggest claim to fame is his cameo appearance in the Disney movie Wreck-It Ralf as a villain.