Short answers, pulled from the story.
Jerry Siegel published a short story titled The Reign of the Superman in January 1933. This early version featured a homeless man named Bill Dunn who gained mind-reading powers from an evil scientist.
Action Comics issue number one hit newsstands on the 18th of April 1938. The copyright date for that issue was registered as the 18th of April 1938.
Between 1938 and 1947, DC Comics paid them together at least $401,194.85 for continued work. They signed a contract on the 1st of March 1938 giving away all copyright rights to Detective Comics Inc without receiving payment beyond $130 for their first story.
The Adventures of Superman radio series began broadcasting in 1940 with Bud Collyer voicing the title character. He also provided the voice for animated shorts produced by Fleischer Studios between 1941 and 1943.
Superman's first appearance is scheduled to enter public domain on the 1st of January 2034. Trademarks will remain protected indefinitely even after the copyright expires.