His name was never mentioned.

After his father died, Charlie and Alan had three step dads. First, a man named Harry Luther Gorsky, who left Charlie and Alan's mother for a young woman, Charlie refers to him as "a little tyrant" (it hints that Harry was a midget). Second was a twitchy gay man from Texas who called him and Alan buckaroos. Third, there was a fat guy with a carpet business, who Charlie liked the most because he had "a grateful daughter".