Mattel has released a Battle Armor Lex Luthor a couple times, but DC Direct made him so much like the old Kenner Super Powers Lex that I found him irresistable. The suit was designed by George Perez, artist for Crisis On Infinite Earths, specifically for the Super Powers toy line, first appearing in Action Comics in 1983.
Lex Luthor is, of course, archenemy of Superman, who teams up with Robot Brainiac in Crisis On Infinite Earths, taking advantage of a Multiverse thrown into chaos by the Anti-Monitor to demand control. Though he has gone through many retcons over the years since first appearing in 1940, Luthor's lack of any superpowers has left him with only his brilliant mind to foil Superman.
Here's Battle-Armor Lex with my Mattel 8" Retro-Action Lex Luthor. I love love love these retro-action dollies, by the way, and have my eye on a couple more...
I also have a most righteous Orange Lantern Lex by DC Direct that I can't believe I haven't opened yet... so many toys, so little time :D
*Lex Luthor at Wikipedia!
*12" Mego Lex Luthor from the 70's!
*Mattel DC Superheroes Battle-Armor Lex (pre DCUC) at OAFE.Net!
*DC Direct Public Enemies Battle-Armor Lex!