Base Breaker: Ingrid. Those who like her think she's cute and a decent fighter atop of that. Those who don't disliked her. The fact that she was a crossover character from a universally-hated game, and her Deus ex Machina storyline didn't help matters at all. This is even more so when it was confirmed that she was the reason the Street Fighter X Tekken conflict happened in the first place. Given both the fanbase's reaction to that game and the box's nature of giving prizes that are either extremely underwhelming or outright screws the winners over, she's really not helping her case any.
Crazy Awesome: Rolento is way fixated with military jargon and utopic dreams, but hey, he can dish it out pretty well.
Charlie. The fact that's he's the Kenny of the series only seems to have bolstered his popularity among the fanbase.
Dan. He quickly became one of the series' signature characters.
Sakura. You don't get your own manga for nothing.
Karin. For a girl who has only appeared in one canonical game and two other games (Capcom Fighting Evolution and Namco × Capcom, where she's paired with Sakura no less), she has a surprisingly large fan following. She is also one of the most fan requested characters for Street Fighter IV, alongside Rainbow Mika, Elena, and Rolento. This is to the point that in an official poll by Capcom, she was rated the #1 most popular character in Japan, even more popular than Ryu himself. Her popularity was likely a factor in her return in Street Fighter V.
Rolento, who was one of the most commonly-requested characters for Super Street Fighter IV and even managed to show up in Street Fighter X Tekken years after his last appearance (Capcom vs. SNK 2), and eventually made it in Ultra Street Fighter IV.
R. Mika has likely reached this status, if not after missing out on SFxT (and thus a long-awaited chance to team up with Zangief), then most certainly after being set up as the butt of a cruel joke alongside Retsu for Decapre's reveal in Ultra Street Fighter IV. She returned in Street Fighter V, much to the delight of her fans.
Epileptic Trees: In Rival Schools (a series with loose ties to SF), there is a character who goes by the name of Ran Hibiki. Given that Hinata learned how to fight by watching a video by Ken and Chairperson practices Saikyo, fans have been wondering if Ran is a relative of Dan's (particularly, his sister).
Fanon Discontinuity: Some fans would rather pretend that Ingrid's appearance in Alpha 3 MAX didn't happen.
Guy in the original Street Fighter Alpha due to his fast and damaging chain combos. He actually cracks a pretty bad joke in SFA3 about how he has his opponent "on a chain" in reference to this.
The crouch cancel bug in SFA3 (basically, being able to cancel longer move recoveries by crouching during a Custom Combo, which made it so that since the character using it never entered a neutral state, their opponent never got an opportunity to flip out of their combo) which made the already powerful V-Ism borderline broken by allowing players to kill their opponents in one long combo.
Germans Love David Hasselhoff: Alpha 2 developed a large competitive following in the United States, especially on the West Coast. This is in contrast to its native Japan where it wasn't received as well, especially compared to its sequel, Alpha 3. It came to the point where it was generally accepted that the U.S. would hands down beat Japan if they ever competed in the game, a reverse of what usually happens.
Launcher of a Thousand Ships: Although Guy is canonically married to Rena (at least by Final Fight: Streetwise), he's been paired with Maki (Rena's sister, and thus his sister-in-law), Rose, and Ibuki, among others. In particular, Guy/Rose is rapidly approaching Fan-Preferred Couple status, thanks in part to their interactions in Super Street Fighter IV.
Memetic Badass: Dan, Master of the Saikyo style, a.k.a. the Strongest Style. The king of taunting and the man in pink. He goes by many names, but you will call him "sensei" today. YAHOO!
Fei Long'sFunny Bruce Lee Noises being typed out and written in SFA3's Story Mode. Having him burst into "WA HOATAAAAAAAAAA!" and other screams is cool when you can hear them, not when you're reading what he says to others.
The dialogue before Yun's final fight with Bison has a rather unfortunate mistranslation, where Bison refers to Yun's arrival and defeat by his hand as "the perfect ending for a third rate actress like Fei-Long."
Final Bison's Final Psycho Crusher from Alpha 3. It does ridiculous amounts of damage regardless of if you block it or not. The only way to avoid it is to use a high-priority move (i.e. Shoryuken), Wall Jump, or, if you're Akuma/Evil Ryu, Ashura Senku it out of there. The first two require critical timing and a lot of luck. On top of that, Bison's boss-exclusive Shadaloo-ism allows him to build meter incredibly fast, meaning he can abuse it multiple times per round if he's feeling nasty. Making matters worse is the fact that if you lose to Bison, that's it. You don't get a chance to continue and try again; it just goes straight to the bad ending.
Final Bison in Street Fighter Alpha 3. Aside from That One Attack above, early versions of the game didn't let the player continue if they lost to him.
Shin Akuma. Basically Akuma without his usual drawbacks in these games.
Too Cool to Live: Charlie, according to Word of God, does everything Guile does but better, demonstrated in-game by his being able to throw Sonic Booms one-handed (or even out of his feet). And we can't have one of Street Fighter's poster boys being overshadowed, can we? Bye bye, Charlie. He eventually came back in Street Fighter V, though.
Uncanny Valley: It may be the style, but some of the artwork done for the series can come across as pretty strange. Take a look at Dan and Zangief in the picture on this article's main page for an example of this.