Who's This? A shape-changing Titan.
How you could have heard of him: The popular Teen Titans Go TV series and movies has Beast Boy as a cast member, and he also appears in Young Justice. He is better known for these animated appearances than in live action, though he has appeared in the Titans TV show (just not as a member).
Example story: Teen Titans Spotlight #9 (April 1987) "Elements of Doom!" by Paul Kupperberg, Dan Jurgens and Gary Martin
What I've learned: Gar doesn't really need to wear a costume because his distinctive coloring is enough and he spends most of the action as a naked animal. I just now noticed he never wears it in this whole issue!
Who's Next? DC's Squirrel Girl (not really).