The ancient Norse god of Thunder.
Superman encounters someone who appears to be Thor in 1948. Thor and his fellow deities Loki and Odin challenge Superman to various contests of strength at the North Pole. However, "Valhalla" turns out to be only a series of props and illusions: a ploy by Miracle Movies to generate publicity for the studio's upcoming film "Northern Lights" (S No. 52, May/Jun 1948).
Sometime later, Jimmy Olsen dreams that in a previous life he was the best friend of Thor during the time of the Vikings. Summoning Thor with his signal gong, "Jimmy the Red" enlists the thunder god's aid in a quest for "Viking pirate treasure" in order to write about his adventure in a saga. During the search, Thor uses his giant hammer to shatter an iceberg before the two adventurers are forced to choose between two potentially deadly fjords. However, before they can choose, Jimmy wakes up from his dream and later learns that his recollection of a past life among the Norsemen was the result of a "hypnotic suggestion" created by conman Swami Rama (SPJO No. 16/1, Oct 1956: "The Three Lives of Jimmy Olsen").