A group of heroes published by DC Comics and created by Jack Kirby. The Challengers of the Unknown first appeared in Showcase #6 in January 1957.

Men have often found that the priorities in their lives are greatly changed with a close brush with death. Many people devote more time to family or their spiritual lives when they look their mortality in the eye. In the case of the members of the Challengers of the Unknown, a single event caused them to rethink the direction of their lives and decide to spend their remaining years on pointless, hair-raising adventures.

While traveling on a small airplane, four men with various backgrounds found their lives nearly cut short. Aboard this plane were Professor Mark Haley (an expert in undersea exploration), Ace Morgan (one of the world's premiere test pilots), Red Ryan (mountain climber and daredevil), and Rocky Davis (the world heavy weight boxing champion). When the plane crashed, the men found that they were unhurt and felt that this was a sign that they should do something. They decided to band together and seek to do good and fight evil, since they felt that they were living on borrowed time. And so, the Challengers of the Unknown were born.

The four had many adventures, fighting evil, giant robots, combatting terrible monsters, and stopping evil geniuses from taking over the world. They were often joined by June Robbins, their token Kirby female, with the Sue Richards hairstyle and varying last name; half of the issues June was not Robbins, but Walters.