Slim was one of Ma Mayhem's boys.
Slim served as the thieving family's safe cracker. He followed his mother in her plan to steal back various pieces of jewelry she had stolen earlier, though somewhat reluctantly. He disliked his mother's plan to only steal the jewelry, while instead they could have stolen items worth more than ten times that.
Slim, along with his brother and mother, also appeared in Batman Beyond #19, "Royal Mayhem", where they kidnap Princess Vinishri of Uganistan.