I know there have been some who may think / complaint that Deadshot isn't a Batman villain (see separate Deadshot as a Batman villain thread), but he did get his start in an issue of Batman back in 1950, and it wasn't until after he reappeared in other Batman stories the 1970s and 1980s that he then became involved with Amanda Waller's Suicide Squad.
First appearance: back in Batman #59 (June-July 1950), though you may not recognize him.
Well, at least appears to have started with good intentions . . .