Origin
Rex was born into the K-9 Army Dog Training Corps just before the United States entered World War Two. He served as a member of the US Army during numerous wars and had an illustrious career. He would later gain some ability to communicate more easily with humans which brought him more closely in line with the mainstream DC Universe.
Creation
Rex’s first appearance was in The Adventures of Rex the Wonder Dog #1 in 1952.
Character Evolution
Rex’s earliest adventures were in the sort same spirit as a lot of fiction which places an animal in the lead role. Over time though the gap between species of the character and the reader has become blurred as he gained the ability to better communicate with humans.
Major Story Arcs
Rex was first conceived as a character for the sub-genre of war comics (one of his litter mates became Pooch in the Losers.) Throughout his golden age and silver age appearances he distinguished himself as a hero in both the Second World War and in Korea (even receiving the Medal of Valor.) His actions extended elsewhere as well. When his original keeper went missing in action he was transferred to the Dennis family in the United States and he helped clear one of the family members of a murder charge. With a move away from war comics in the silver age, he was partially reconceived as a general character partaking in random adventures, part of which he took part in with Danny Dennis, one of the members of his foster family. He spent time after this in a variety of positions such as a Hollywood stunt dog as forest ranger. He even experienced some more fantastical journeys through time and to other dimensions (to Skartaris). His most important was a journey with Detective Chimp to the Fountain of Youth in Florida and after drinking from it he receives eternal life. After this his renewed youth and vigor lent itself to new adventures, which would eventually take him and Danny to the moon.
Rex came back to prominence during the events of Day of Vengeance as he forms an alliance with Detective Chimp after the Spectre destroyed the Rock of Eternity.
Later Rex is approached by Congorilla and Mikaal Thomas while he is working for NASA in their space program. His owner is now Colonel Dennis and he can no longer communicate with humans as effectively. He is enlisted to helped stop a fringe group of gorillas intent on taking over Gorilla City by using the scientific knowledge of Malavar. He had been a fugitive from them while he was trying to revive the Tasmanian Devil in a Lazarus Pit. They soon after joined forces briefly with the Justice League of America.
Powers and Abilities
Rex is an otherwise normal dog, who has been granted the ability to better communicate with humans and eternal life. As a dog he exhibits the usual characteristics associated with the species including a speed beyond that of humans in short distances and increased hearing. Although not always able to communicate with humans, his actions have proven him a capable leader on numerous occasions.