Walter Gripp is the protagonist of the short story The Silent Towns. This is part of Bradbury's collected work The Martian Chronicles.
Gripp's story takes place in the later years covered by Chronicles, following the outbreak of a nuclear war on Earth. This war was introduced in The Off Season, when Sam Parkhill sees the Earth "catch fire", and continued in The Watchers, where the Martian colonists receive signals from Earth that indicate a catastrophic war has begun, ending with the enigmatic message "come home". This is a strange calling, as it can represent both the fact that the colonists still see Earth as their true home, but also as a lemming-like summons to die needlessly. Most of the colonists return to Earth, leaving only Walter Gripp, or so he thinks.
Gripp only came to town every week or two, because he lived in a shack in the hills and worked in a placer mine. The town's abandonment was a complete surprise to him.