Lionel Luthor is a shrewd businessman who was the owner of Luthorcorp in the television series Smallville. He's famous for being the father of Lex Luthor. He's also a member of a secret society called Veritas.
The television series show him as a ruthless businessman, albeit shrewd and not without redeeming qualities. He had raised Lex Luthor with a classical education, which is further shown that he had another son named Julian, who died at a young age before the series' beginning. It was later revealed that Lex's proper name is Alexander Luthor, to which he was named after Alexander the Great, and likewise Julian was named in honor of Julius Ceasar. Lionel Luthor is also shown as an eccentric, wearing long hair which he wears without hairdressing, as well as a beard. This is for two reasons, one that as the head of a company he can make his own decisions about personal appearance and two that he is portrayed as an antithesis of Lex Luthor, who is bald and clean shaven.
The season finale for the first season shows Lionel and Lex in a bidding war in an effort for Lex to stop being so focused on the small branch of Luthorcorp in Smallville and move on to bigger and better things in Metropolis. Lionel closes down the Smallville factory, citing budget cutbacks. Lex makes an attempt to save the Smallville workers by draining his trust fund to buy 90% of the factory, then rallies the bosses to put up the rest. When the managers worry about the risk involved, Lex reminds them this is a chance for their hard work to pay off; that as part owners of the factory they would now be lining their own pockets, not Lionel's.
Although Jonathan Kent despises Lionel Luthor, apparently Luthor does not have the same hatred for Johnathan. In one episode when Clark's attitude was soured by Kryptonite, he attempted to go rogue and harm a temporarily blinded Lionel. Lionel Luthor successfully talks Clark out of doing so by saying that Jonathan and Martha Kent are "hardworking, salt of the earth people" and that he would wonder how they would react to their son trying to harm him. Although this may have been a means for Lionel to make Clark think twice about hurting him, this does strongly suggest Lionel Luthor has some empathy and respect for the plight and values of the Kents.
In the comic book continuity, he is not the owner of Luthorcorp but is still Lex's father.