This event attracts athletes who seek to explore the extreme in physical and mental abilities. The race is limited to 35 athletes on an invitation-only basis and attracts participants from around the world, including Brazil, Canada, Italy, Puerto Rico, Spain, Sweden, Slovenia and the United States. Racers must have reached their 20th birthday prior to the start of stage one. Each racer must be accompanied by an individual support team of at least two people over the entire course. Many support team members are volunteers from the Big Island community.
The Ultraman Challenge has been held annually since 1983 over Thanksgiving weekend as an extreme offshoot of the Ironman. The Ultraman is a sanctioned triathlon by the Triathlon Federation/USA and takes the components of the Ironman to the limits. The popularity of races such as the Ironman and Ultraman helped to establish the triathlon as an Olympic sport. The Olympic Committee included the triathlon as an event during the 2000 Summer games in Sydney, Australia, in the form of swimming, biking and running.