Who is Pickard from The Illustrated Man and what is their importance?

Pickard is a character in The Long Rain. Over the course of the story, he goes insane while in the jungles of Venus. He uses his gun to shoot at the rain, seeming as if he is trying to kill it. Later, he goes into a coma. Simmons chooses to kill Pickard rather than leave him to drown in the rain that made him crazy or carry him along.