En route by plane to appear on the radio program "Heroes," Olympic wrestling champion Lester "Rocky" Davis, master skin diver Walter "Prof" Haley, circus daredevil Matthew "Red" Ryan and War hero and jet pilot Kyle "Ace" Morgan, are caught in a storm and their plane crashes. Surviving the crash, the group agrees that they are living on borrowed time and they should working together, challenging the unknown as a team.
After making headlines with their exploits, the Challengers of the Unknown are offered a million dollars by the mysterious Mr. Morelian if they succeed in opening a Pandora's box. Taking the box out to an uninhabited island, each member tries opening the box. The team members unleash and stop terrors such as a giant stone warrior, a miniature sun and a whirling weaver. Afterward, Morelian appears, informing them that he knew of the dangers in the box, and set the Challengers to release them so he could get the true prize of the box: A ring of immortality. However, when Morelian tries to fly away, his plane crashes and he dies, the ring having been nonfunctional. The Challengers leave the island, wondering where their next adventure will take them.
Soon famous, the Challengers accept many "unknown challenges" from The Pentagon, mad scientists, and people with problems. Over time the Challengers establish the hollowed-out Challengers Mountain as headquarters. Later, they adopt an hourglass logo to symbolize time running out. They encounter genies, common and sophisticated thieves, fantastical creatures, aliens and robots. Their adventures later veer toward superheroics, and range in scope from occult menaces to unknown phenomena. The Challengers travel through space, time and other dimensions. They encounter the likes of the Doom Patrol, Deadman, Swamp Thing, Johnny Double, and the Sea Devils, with whom they fight the criminal group Scorpio. June Robbins, a computer genius and archaeologist, joined the Challengers for many adventures as an "honorary" or "girl" Challenger.
When Red is killed, a teen rock star/engineering genius immediately wages a vendetta against the three-man team. "Tino Mannaray" turns out to be Martin Ryan, Red's kid brother, who blames the team for his brother's death. Red eventually returns. Though blown up, he had been dosed with shape-changing Liquid Light and rendered amnesiac, and nearly conquered the Pacific while believing himself to be a Tiki god.
As the team's challenges become more occult in nature, Red's brother Tino is blinded. Red donates an eye to his brother and dons an eye patch. Eventually, Red receives an eye transplant. Prof becomes possessed by an evil spirit and is shot by a villain. While he recovers, Corinna Stark, a mysterious blonde with mystical knowledge, invites herself onto the team. The Challengers fight occult alien-monsters in backwoods villages and dark dreams, and Rocky and Red fight for Corinna's affection.
The Challs are later semi-retired, their mountain a theme park, and their adventures disregarded as cooked-up articles in a tabloid, The Tattletale. The nearby town has renamed itself Challengerville, managing to thrive on the team's name. A cosmic entity, which prides itself as "the personification of all evil," influences the entity Multi-Man to blow up the mountain. The town is destroyed. Hundreds die, including, Prof and June. The surviving Challengers are placed on trial, but eventually freed with the testimony of Superman. They are, however, ordered to disband.
A tabloid reporter, Harold Moffet, becomes involved with the group after several unexplained incidents. Moffet began to piece together many seemingly unrelated massacres. Red became a violent, vigilante mercenary. Ace became an addled mystic, losing new-found friends due to inattention and incompetence. Rocky became lost in a life of luxury and ended up in an insane asylum.
After some time, the three reunited and with Moffet's aid, found a strange portal near what was once Challengerville. They discovered Prof and the pregnant June, alive in a strange 'phantom zone.' The dark demon confronted them and the final battle came down to Moffet and one neutron bomb. The decision to attack was taken out of Moffet's hands by Multi-Man, who sacrificed himself to destroy the demon.
"The New Challengers of the Unknown," including ghostly Prof and June, were poised to take on menaces in the dark corners of the world.
Later, four new Challengers pursued more unusual and occult horrors. They are Clay Brody, NASCAR driver; Brenda Ruskin, physicist; Kenn Kawa, radical games designer; and Marlon Corbet, commercial pilot. This team was also born after miraculously surviving a plane crash. They stopped sacrificial wackos, drug-juiced zombies, vengeful ghosts, Amazonian cults, Lovecraftian monsters, mass suicides, humming buildings, and other oddities. They were advised by original team member Rocky Davis, older and grayer and alone. It was eventually revealed that the original Challengers had been dematerialized by a mad scientist's ray-weapon. The same ray caused both plane crashes, as well as others. Soon the original Challengers reappeared, helped the young Challengers defeat the madman, before walking back into oblivion (minus a wounded Rocky) to shut down a runaway Tesla field. The young Challengers vowed to fight on.
Superboy discovers the missing Challengers—Ace, Red, Prof, and June—in Hypertime. The team had been waging guerrilla war against Black Zero (a Superboy variant). With Black Zero defeated, the team returns to Earth, but loses Red along the way. Reunited with Rocky in Metropolis and hosted by Rip Hunter, the original Challengers vow to explore Hypertime, "the greatest unknown," in an attempt to find Red.
Two Challengers partake in Infinite Crisis. Rocky Davis and Prof Haley help stem the escape of prisoners from Blackgate Penitentiary. Rocky fights in the Battle of Metropolis. He is one of dozens of heroes fighting the opposing army of the Society. The Society is ultimately defeated.
After the Infinite Crisis, the Challengers reformed partially, to man a space station and scan for a group of heroes who were lost in space.
Equipment: None known.
Transportation: Both of the first two Challengers teams had jet planes. The first team's first plane was the Challenger SST.
Weapons: None known.
- The original Challengers were scheduled to appear on the radio programme. When the origin was re-told in 1965, that was changed to a television show.
- Their original origin stated that the plane crash was so devastating that even Red's watch was shattered and had stopped. Various recountings over the years occasionally changed that to having Red's watch survive the crash intact.
- Showcase #6 describes Ace as a heroic pilot during "the war", which war was left unsaid. In Challengers Vol 1 45, it was established that Ace was a US-AAF pilot during World War II. Later, in order to account for the passing of time without aging, his aviation heroics took place while he was a USAF jet pilot in the Korean War.
- Prof started as a master skin diver; however, within a dozen issues, that evolved to where oceanography was only his principle field and he was a genius in a large number of scientific fields.
- Red was initially presented as an expert mountain climber. Since, like Prof, that was a limiting field, it was established that he was also an electronics expert. Toward the end of the original series, to expand his talents even further, it was established that Red was raised in a circus and he had developed the all-around skills of a circus acrobat.
- There is a story that, on a world without superheroes, a blogger, a hip hop artist, an eco-terrorist, and two others discover they have been genetically enhanced and chip-programmed to be soldier-pawns by the Hegemony, a cabal of billionaires who secretly run that world. Made slaves on a Moon base, three Challengers blow up the base, escape to Earth, and declare war on the Hegemony until (like a group of obliquely mentioned earlier Challengers) their "borrowed time" runs out.