James Garner and Jack Kelly in the original series. There was a remake in the 80's I think that was kinda lame.
I think Efrem Zimbalist Jr. (from "The FBI") appeared in the original series as another brother . . . and I vaguely remember an episode with yet a fourth Maverick brother, but don't remember who played him. And of course Roger Moore was a Maverick cousin.
I thought the remake series ("Bret Maverick" also starring James Garner) was decent, especially the episode in which it was revealed that Maverick carried about a dozen or so "hideout" guns . . .
IIRC, this show had respectable ratings, but someone at the network didn't like it and cancelled it. (Around the same time, they kept "Love Sidney" on the air longer, which possibly said something about who was running the network.)
"Young Maverick" with some nobody in the title role
was disappointingly lame and got promptly cancelled.