He's an X-Man. He's the King of Thieves. He's Gambit!
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Art by Clay Mann
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Art by Adi Granov
First appearing in Uncanny X-Men #266, Gambit was created by Chris Claremont and Jim Lee and has become a fan-favorite of the X-Universe, appearing in many X-Men titles as well as a slew of his own solos (which have explored his history with the Thieves Guild). He has most recently been in Excalibur with his long-time love and recent wife, Rogue, who also appeared with him in Mr. and Mrs. X as well as Rogue & Gambit. Some of his essential reading includes:
Uncanny X-Men #266, 267
X-Men Vol 2 (issue 33, in particular)
Any of his solo series (but I personally prefer the Nicieza series and the Asmus series)
Mr. and Mrs. X
Rogue & Gambit
Astonishing X-Men by Marjorie Liu
X-Treme X-Men Vol 1 by Claremont
X-23 by Marjorie Liu
(If anyone has a more comprehensive list of essentials for reading Gambit, please share and I can edit this).
He is known for his signature use of playing cards, which he charges with kinetic energy, as well as a bo staff and his athletic abilities (not to mention his skills as a master thief and a bit of a womanizer).
Gambit gained a lot of his popularity as a main cast member in X-Men: The Animated Series, but he has also been in X-Men Evolution as well as Wolverine and the X-Men. He has also appeared in X-Men Origins: Wolverine and was slated to have his own feature film, which has been shelved. Recently, he was portrayed by Bill Heck in the podcast, Wolverine: The Lost Trail.
Other than Rogue, Gambit is friends with Storm, X-23, somewhat frienemies with Wolverine and Deadpool and has a complicated relationship with Mr. Sinister.
That's all I've got for him, but if you're a fan, you probably know all of this already and more!