Iron Maiden (not the metal group nor the torture device)
Wally Wood's Iron Maiden was a freelance criminal who worked for various eeevyil masterminds and pulled a few schemes with her own gang in the Tower Comics' T.H.U.N.D.E.R. AGENTS starting back in 1965. We never learned anything about her past, she was just there in her armor, cloak and gun. "Rusty" had the typically bantering attraction/distrust relationship going on with Dynamo that so often happens between uptight super-heroes and attractive villains. Iron Maiden had a wry awareness about how unworkable an affair between them would be, but she found the big lug very sexy and enjoyed teasing him and trying to bring him over beyond the law. On his side, Dynamo was a bit more confused about his feelings; the fact that Iron Maiden had him framed for treason and put in other sticky spots was something he understandably held against her. Yet they also sometimes covered to let the other escape at the end of an adventure. It was a typical crazy mixed-up quasi-romance. (Comic fans will likely find Batman and Catwoman coming to mind as the classic example.)
I like the way Rusty is frequently shown with a cigarette. By the late 1960s, smoking was becoming rarer in comics except for a few tough-guy heroes at Marvel. It adds to her bad-girl image. She did go to jail a few times (her gang broke her out in one case). The original run of T.H.U.N.D.E.R. AGENTS ended with her still up to her felonious tricks; since then, copyright ownership was disputed and a number of publishers did their own riffs on the series, but that's outside my area.
Looking over some of these stories, I was struck that this sort of friendly enemy set-up was not original with comics. Thrillers and crime fiction had any number of roguish jewel thieves and cat burglars and con men who robbed unpleasant wealthy people (so it seemed almost harmless) and the police often seemed to like the crook better than the victim. Leslie Charteris' marvelous stories of the Saint from the early 1930s had a lot of this. Scotland Yard bulldog Inspector Teal grew to become friends with Simon Templar, much to the latter's surprise. After a few years, the Saint would be seen having a few drinks or dinner with Teal and even volunteering to help solve a few crimes if he was bored. This, despite the fact that Tenmplar himself was one of the most notorious outlaws in Europe ("the Robin Hood of Modern Crime"). There have been quite a few similar pairings, not to mention all the Phillip Marlowe-type detectives who have a few lifelong pals on the shady side.