Paranormal explorers the Challengers of the Unknown got their own title following their test run which began in Showcase# 6 (February 1957). Following the adventures of Rocky, Red, Ace and Prof, the series ran for 87 issues. The first issue features cover and interior artwork by Jack Kirby and the "King" also wrote both stories, "The Man Who Tampered With Infinity" and " The Human Pets." The first issue set the tone for the 86 that were to follow. In the Challenger's adventures, the non super hero adventure comic reached its peak. Many see in Kirby's interpretation of the team the inspiration for and even prototype of the Fantastic Four. The team would later re-appear in three new self - titled series, which varied widely in tone and interpretation of the team.