Richard Matheson was decidedly one of the Grand Masters. I'd put him in the same category as Ray Bradbury and Isaac Asimov without hesitation. Over his lifetime he worked in fiction, television and movies and his influence was bloody near everywhere.
What Dreams May Come, The Shrinking Man, A Stir of Echoes (A book I've read easily a dozen times), I Am Legend, Bid Time Return. He wrote the screenplay for THE NIGHT STALKER, upon which the series Kolchak: The Night Stalker was based. He wrote multiple episodes for THE TWILIGHT ZONE, Worked on STAR TREK the original series, THE NIGHT GALLER, and wrote the script for a TV movie called DUEL, that was directed by a young director, just starting out, named Stephen Spielberg.
He was a truly amazing writer of the fantastic and I will always remember his works fondly. He will be missed.