The greatest conquerer in the history of the Disc, his empire spanned the entire world with the exception of the Counterweight Continent and XXXX. It is said that when he reached the shore of Muntab, "Carelinus wept, for there were no more worlds to conquer." Cohen respects the thought, if not the tears. With his life history and the stories about him, he is the Discworld's answer to Alexander the Great.
Famous for untying the Tsortean Knot by cutting through it with a sharp sword. This may be considered cheating by some, but as Cohen pointed out upon being told the story, it was a really big sword, and there was this great army right outside the door, and maybe telling him that wouldn't be the best idea...
After his death, his sons squabbled over his empire, which eventually disintegrated because of this.
Presumably, Carelinus did not follow in (well, precede) Cohen's footsteps and hijack a Valkyrie's horse so as to get to - and conquer - the other worlds that are out there. You never know, though.
Carelinus is directly based on the historical figure Alexander the Great. Alexander was widely recognized for conquering most of the known world of his time, and for various dramatic flourishes of dubious historical accuracy, but nevertheless, as Cohen points out, they make a good story.
The Tsortean knot is a version of Alexander's famous solution of the Gordian knot, a supposedly impossible puzzle which he cuts through with his sword, as recorded by his biographer Arrian. Generally the story is told as an illustration of creative thinking - when the immediate solution does not present itself, an unconventional method may prove most useful.
The lament of Carelinus is also taken directly from the legends of Alexander, although it is not attested in his biography, may be derived from a passage in Plutarch: "Alexander wept when he heard Anaxarchus discourse about an infinite number of worlds, and when his friends inquired what ailed him, "Is it not worthy of tears," he said, "that, when the number of worlds is infinite, we have not yet become lords of a single one?" Theologian John Calvin may have been responsible for turning this into a quotable saying, as he paraphrases Alexander: "hearing that there were other worlds, wept that he had not yet conquered one."
Carelinus's name may also be a pun on Charlemagne, another historical conqeror, also known as "Carolus".