While most people don't know exactly where Odie came from in the Garfield comic strip, the common belief is that he was around since the first strip. Odie actually joined the strip on August 8th, 1979 one day after his original owner, Lyman, joined the cast.
Yes, Odie was originally owned by a friend of Jon's who lived with him and Garfield for a few years. Lyman was originally meant to be someone Jon could talk to and confide in, but Garfield soon filled that role more and more rendering Lyman obsolete. Lyman quietly disappeared from the comic in 1983 with a final appearance in 1988, leaving Odie in the care of Jon.
As to what happened to Lyman? No one knows for sure. Jim Davis, creator of the strip, has put forward two different situations: Either Lyman joined the Peace Corp or his corpse currently resides in Jon's basement. No fooling, Jim Davis has said "don't look in Jon's basement" when asked what happened to Lyman.
