Rex was born into the K-9 Army Dod Trainingg Corps, just before the United States entered World War Two. One of his litter brothers would grow up to be Pooch of the Losers.

Rex distinguished himself during the War and in Korea was awarded a medal of valor. When his original master was pronounced missing in action, Rex was shipped stateside to live with the Dennis family. But Philip Dennis was under indictment for murder, so Rex sniffed out the real murderer and frightened him into confessing.

However, it was Philip's brother Danny who quickly established a rapport with Rex. Together they travelled the world. Rex spent time as a Hollywood stunt dog and as a forest ranger; he even journeyed into the dimensional land of Skartaris, years before Travis Morgan "discovered" it.

Eventually, the years and the adventures began to take their toll on Rex. He and Danny were reduced to performing tricks for benefits. Fortunately, Rex met Bobo the chimp (Detective Chimp) and the two animals inadvertantly drank from the fountain of youth. Rex returned to prominence and within a few short years, he and Danny were walking on the Moon.

Day Of Vengance

During the Specteres reign the rock of eternity was destroyed freeing the seven sins so the could inhabit humans. Rex stayed behind with Dectective Chimp exclaiming he dosent want to have to fight then wash the blood out've his teeth when its over. The sin of Lazyness had possesed him and Dectective chimp lay down the bottle to free him from the sin of Lazyness.