After the cancellation, Rex did not appear again for another 18 years, until he was re-introduced by writer Steve Englehart in Justice League of America #144 (July 1977), a flashback issue to 1960 which featured a number of minor 1950s DC Comics characters that had once had their own series.

After this there were only sporadic appearances: a 'Whatever happened to ...' tale in DC Comics Presents #35 (July 1981) written by Mike Tiefenbacher with art by Gil Kane,[5] Secret Origins #48 (April 1990), The Flash (vol.

Rex is a white shepherd dog who spent his early years in the U.S. Army's K-9 Corps, alongside his brother, Pooch.

Early in his training it became apparent that Rex had great potential, which resulted in Dr. Anabolus selecting him as a test subject for a super-soldier serum.

After receiving an injection of the serum, Rex found himself endowed with great strength, speed, stamina, and intelligence.

Over the next few years, as well as solving a never-ending series of burglaries, robberies, murders and other crimes, becoming a film star and a circus actor, and daring natural disasters such as forest fires and thick snow, Rex also managed to survive attacks from lions, wolves, bears, panthers, and even octopuses (twice).

Many of Rex's adventures took place in the American Midwest, but a number happened in Europe, Asia and especially Africa (largely as a result of Major Dennis being involved in various archaeological expeditions).

While staying with a scientist friend of the family, John Rayburn, who created a formula to shrink living beings to microscopic size.

[27] Around this time, Rex was involved in thwarting an attempted invasion of Earth by Martians with the future founding members of the Justice League of America: The Flash, Superman, Wonder Woman, Batman and Green Lantern, among others.

[28] After this, he and Danny Dennis became a circus act for many years,[29] where Detective Chimp came to see them and got involved in an adventure with a now obviously aging Rex.

[31] No reason was given for this new ability, but shortly afterwards Rex joined 'The Bureau of Amplified Animals', an organisation of animals with abnormally high intellect run by Detective Chimp to help mankind, and was instrumental in defeating Grodd again,[32][33] also revealing that he can speak, and possesses 'the knowledge of force of mind, and how to use it'.

Without Rex's powers, Pooch followed Gunner and Sarge through thick and thin, was wounded multiple times and received the honorary rank of Sergeant.

He has also exhibited unspecified other enhanced powers as a result of this, and is acknowledged as a member of DC's magical and mystical community.