Father of Cligés and actual hero of the first third of the romance bearing his son's name, Sir Alexander seems to have spent much more time than Cligés did as one of Arthur's knights.
The older son of the Emperor of Greece and Constantinople (who was also named Alexander) and his Empress, Tantalis, Alexander was already grown by the time his brother Alis was born. Young Alexander might have ruled Greece, but he insisted on receiving his knighthood from the great King Arthur and no one else. For this reason he journeyed to Britain, where he hoped to win fame and honor. He brought a dozen warrior companions: Cornix, Licorides, Nabunal of Mycene, Acorionde of Athens, Ferolin of Salonica, Calcedor from Africa, Parmenides, Francagel, Torin, Pinabel, Nerius, and Neriolis. Arthur welcomed them into his court at once.
When Count Angrs of Windsor rebelled against Arthur, who was summering in Brittany that year, Alexander and his companions chose the moment to request knighthood, which Arthur granted them; they used the water of the English Channel for their ritual bath.
Alexander and his companions proceeded to put down the rebellion and Alexander himself captured Angrs of Windsor, who led the revolt, for which Arthur rewarded him with the kingdom of Wales to hold until he should inherit Greece, while Guenevere wisely sped his hesitant courtship so that he and Soredamors could wed without further delay. Cligés was born about fourteen months later.
Meanwhile, the old Emperor of Greece died commanding a search for his firstborn son; the ship sank on its way to Britain, and the single survivor, favoring Alis, made his way home with the medacious report to the noblemen that it had sunk on its way back, drowning Alexander with everyone else. Consequently, Alis was crowned emperor. When Alexander learned of this, he returned to Greece with his wife and young son, prepared to go to war for his rights. A compromise was effected whereby Alis kept the title, on condition of never marrying, while Alexander did the actual ruling.
Perhaps in the tradition that was later to include Tirant lo Blanc and Don Quixote himself, Alexander died of sickness. Cligés was just about old enough to attend his father's sickbed and receive the parental charge to prove his prowess in Britain. Soredamors soon followed her husband in death, and Cligés had to struggle against Alis for the throne of Constantinople.
It is possible that Chrétien's knight transmogrified over the centuries into Malory's Alisander le Orphelin, though their life histories keep them separate characters.