Lin Carter's Thongor was a paperback series first, then a short-lived Marvel comic series. John Jakes' Brak, too.

There was a comic of Brian Lumley's Harry Keogh / Necroscope in the '90's. And if we're gonna bend the rules to include characters that appeared in hardcover novels that were then reprinted in paperback, then adapted to comics -- Anne Rice's Lestat.