The original team was formed after the end of World War III, which ended on October 29, 1986. The atomic war lasted a mere twenty days. As a result of its aftermath all plant life and animals were destroyed. There was no functioning governments or rules of law and the shapes of the continents were changed. The only food left behind was what was left in storehouses. The original team consisted of an ex-soldier Gardner Grayle who was the group's leader. The second member to join was former school teacher Douglas Herald. The third and fourth members to join were the ex-soldiers and brothers Hollis and Wayne Hobard. The fifth member to join was one of Earth's last remaining scientist Bryndon Smith. The final member to join was Marene Herald the sister of Douglas Herald. The Atomic Knights wore ancient suits of armor from a museum because the armor protected them from the radioactive power of the R-Grenades and Raguns (radiation guns).
The original Atomic Knights were created by editor Julius Schwartz, writer John Broome and artist Murphy Anderson. Their first appearance was in Strange Adventures #117.
Originally the adventures of the Atomic Knights were depicted as set in an alternate future designed earth-86, but this was retconned in 1983, when Grayle was integrated to the main universe. All the adventures lived in earth-86 were considered as a virtual reality dream of Grayle.
The Post-Crisis Atomic Knights are a resistance group fighting against the government agency S.H.A.D.E. After the city of Bludhaven is nuked it is taken over by the government. The Atomic Knights' goal was to protect the city without having to rely on the government and the corrupt Father Time. They operate from an underground bunker designated Command D.
During the Countdown to Final Crisis, Una, Karate Kid and Firestorm come to Bludhaven and come across and fight the Atomic Knights. During Final Crisis the Atomic Knights defend Bludhaven again when the now barren Bludhaven becomes the beachhead for Darkseid's invasion of Earth. They battle a possessed Mary Marvel and Marene Herald is killed. Finally they fell after the final attack of the justifiers.
When the Multiverse was recreated at the end of Infinite Crisis, the Earth designated as Earth-17 showed a post apocalyptic landscape that was guarded by the Atomic Knights, similar to their pre-Crisis appearance. In Multiversity it was revealed than the Atomic Knights now resemble members of the Justice League and are being lead by Captain Adam Strange. If they have some connection to the original Atomic Knights is yet to be revealed.
In Countdown: Arena another team called Atomic Knights made a brief appearance. They were a group of soldiers similar to Captain Atom and came from pre-Flashpoint earth-38. They were killed along with other Captain Atom doppelgangers by Monarch. Post Flashpoint their whereabbouts are unknown.