I think he was a mad scientist first and then later became an industrialist.
Yes, in the comics from the '40s through the '80s he was a scientific genius who used his brilliance for crime and for battling Superman. He actually became a somewhat sympathetic character, someone who could've done great good if he hadn't developed hatred and jealousy of Superman (or the belief that Superman's existence was a threat to humanity) and turned to crime in order to battle him. Then, when the continuity was restarted in '86 or thereabouts, Lex was reinterpreted as a corporate mogul who owned most of Metropolis and had all the best scientists on his payroll. Since then, he's increasingly been portrayed as a mix of both; for instance, in Superman: The Animated Series
, Lex started out as the business mogul, but "Ghost in the Machine" established that he was actually a gifted scientist as well, and later in Justice League
he was portrayed more along the classic evil genius/high-tech criminal lines, at least until he "reformed" and went into politics. And in the comics these days he's portrayed as both mogul and scientist, I believe.