If it was mentioned at all, it would probably be either in Green Green Glow of Home, or Strange Visitor. I haven't seen the episodes in a long long time, though. (finds transcript of GGGoH) Not there.. can't find one for Strange Visitor yet, though.

"You need me. You wouldn't be much of a hero without a villain. And you do love being the hero, don't you. The cheering children, the swooning women, you love it so much, it's made you my most reliable accomplice." -- Lex Luthor to Superman, Question Authority, Justice League Unlimited