Aldebaran was the guardian of Taurus Temple, and the Taurus Gold Saint. He had not an important participation in the story.
Aldebaran is a stern man, but have a noble justice sense. But, because his noble justice sense, he became a servant of Athena, but follow an Athena that didn't exist; the pope, induced Aldebaran to follow your evil schemes.
When Aldebaran news of murders of Pope servant's, he presumed that these servants saw the Pope's face and killed right after; Aldebaran was in doubt about the pope, thought he was hidingsomething or was not the true pope. In the Sanctuary invasion, Saori Kido gets in trouble, and Aldebaran defeated Shiryu, Hyoga and Shun, but, because his doubt, don't' smash them instantly, and presumed Saori Kido could be Athena, and the traitors Bronze Saints, your servants. Seiya swears cut one of the two horns of Taurus Cloth helmet. Aldebaran promises to let Seiya and his friends cross the Taurus Temple, if Seiya does this miracle.
Seiya discovery the Aldebaran foible, and cuts his left horn. In the manga, Aldebaran, in doubt, lets Seiya, Shiryu, Hyoga and Shun cross the Taurus Temple, but, in the anime, he lets only Seiya to cross the temple, and challenge the other saints, playing with them. After the four bronze saints across the Taurus House, Aldebaran, in doubt, wait the war's end, and when discovering the truth about the Pope and Saori Kido, instantly, swear loyalty to her, because his justice sense
Aldebaran possesses Cosmo and the seven sense, the most powerful cosmic in the canonical series. He is the strongest gold saint in brute force, and can smash anyone with the basic specialability of him (Great Horn), but, with a foible.