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. Dr. Anabolus was killed by a Nazi spy soon after, and as Anabolus left no records, this led to Rex being the only dog of his kind. Rex served during World War II, acting during the Italian campaign and earning an unspecified medal for saving his handler Lieutenant Dennis from a German patrol, and later receiving a
Silver Star for saving
POWs. He and then Captain, later Major, Dennis followed this by serving in the Pacific campaign against
Japan, and later in
Korea. After his army career, Rex was adopted by Major Dennis and his family. Not long after moving into his new home, Rex began a new career as a crime solver when Dennis's son Phillip was accused of murder and, when the police were unable to solve the crime, Rex succeeded in finding all the requisite clues to clear Phillip's name. Soon after, he was made an honorary
Forest Ranger In most of his subsequent adventures, he would be seen accompanying Phillip's younger brother Danny. 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). He could ride a horse, or bull, and proved an expert bullfighter. He often operated small appliances such as cameras, swung on ropes and vines to save people. 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). Rex added to his military medals when he was decorated for bravery by the
French Foreign Legion in
North Africa, after one of several adventures with them, and added further to his awards when he became an honorary
Native American Indian Chief, and fought frozen
mammoths on several occasions. In
Australia he met an alien, Xstar, and helped him recapture an escaped creature. He soon met Xstar again to solve an outer space crime becoming 'Wonder Dog of Earth' in the process. While staying with a scientist friend of the family, John Rayburn, who created a formula to shrink living beings to microscopic size. They had a number of adventures at a much-reduced size in a sub-atomic world. Pre-empting
Ray Palmer, The Atom by over a year, using the formula in reverse, they had several adventures in a giant-sized 'super-atomic world'. 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. After this, he and Danny Dennis became a circus act for many years, where
Detective Chimp came to see them and got involved in an adventure with an aging Rex. Taken to the Caribbean, Rex and Detective Chimp accidentally drank from the lost
Fountain of Youth and were both rejuvenated. Some years later, Lt. Colonel Daniel Dennis and Rex became part of a U.S. Moon landing team, Rex becoming 'America's first Wonder Dog on The Moon' in the process. By 1991, it became clear that more than a new lease of life had happened to Rex. While saving the world from
Gorilla Grodd, 'the dog at the heart of the world, the dog for whom the universe has waited' (as he now described himself) confidently communicated with the newly sentient animals of Central City, and persuaded them to fight against Grodd. 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, also revealing that he can speak, and possesses 'the knowledge of force of mind, and how to use it'.
Working without Danny At some point after this, it appears that Danny and Rex parted company, as the now ageing Danny does not feature in Rex's later adventures. After being (accidentally) involved in a fight between almost every DC hero and many villains at the opening of
Guy Gardner's bar 'Warriors', Rex later became attached to
Hero Cruz (also known as HERO) sometime before he became a member of 'Superboy and The Ravers', and lived with him in
Metropolis. Hero, owner of the "H-Dial" from '
Dial H for Hero', later made reference to having discovered Rex imprisoned in a metal box. It is known that Hero found the H-Dial and other heroic relics after breaking into a weapons cache owned by the villainous
Scavenger; but it is unknown whether, although likely that, Rex had previously been captured and was found during the same raid. Rex's part in the Ravers adventures was minor, and showed little of his powers. How long he stayed with Hero afterwards is unknown, but Rex was next seen, without Hero, assisting the mystical team Shadowpact in battling the Seven Deadly Enemies of Man, which had been loosed in
Gotham City. During this event, Rex was taken over by the entity known as 'Sloth' a situation rectified by his friend Detective Chimp. Shortly afterwards it is confirmed that Rex held a place in DCs pantheon of mystical powered characters when first he was called as one of Earth's most powerful magical characters to aid the
Spectre in saving the universe. Soon after he is one of the many agents tasked by the
Phantom Stranger to monitor a mystical bubble that contained the town of Riverrock, Wyoming and the newly formed Shadowpact vowing to stay until Detective Chimp was freed, and as a result ended up staying a year. The Shadowpact free themselves through other means. He later deliberately allows himself to be influenced by the
Huntsman's Hellhound Pack to infiltrate them, but became trapped with the pack, and spent a considerable amount of time using his intelligence to become their leader, although he eventually aided Shadowpact to beat The Huntsman and return to Earth.
Relatives His brother, Billy, affectionately known as 'Pooch', became the mascot of Gunner and Sarge of '
Losers' during World War II. His adventures were documented in '
Our Fighting Forces' and several series of 'The Losers' for DC Comics and the Vertigo imprint. 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 perished alongside Gunner, Sarge, and The Losers near the end of World War II. An alternate-universe story places the death of those heroes on
Dinosaur Island. ==Powers and abilities==