THE OMEGA MAN was a remake of the 1964 film LAST MAN ON EARTH starting Vincent Price, which was based on the 1954 novel I AM LEGEND written by Richard Matheson. The novel is better than any of the films.
He also wrote a number of other books which were adapted to films:
Legend of Hell House
Somewhere In Time
Incredible Shrinking Man
What Dreams May Come
Real Steel
He also wrote 16 episodes for The Twilight Zone, including Nightmare at 20,000 Feet.I