In the anime:
- Host of Campania: Alois is the host of the Campania, a luxury liner, where he holds a social event attended by the main characters, Ciel Phantomhive and Sebastian Michaelis. His true identity is revealed as the younger brother of Ciel's father, Vincent.
In the manga:
- Relative of the Trancy family: Alois is the heir to the Trancy Earldom, a noble household. He is manipulated by his butler, Claude Faustus, who is actually a demon trying to resurrect his master. Alois forms a contract with Claude, gaining demonic abilities.
- Ciel's rival: Alois becomes Ciel's rival and seeks revenge on Ciel and Sebastian, believing they are responsible for the death of his brother, Luka. He plots to destroy the Phantomhive estate and take control of the underworld.
- Past trauma: It is revealed that Alois had a traumatic past involving abuse and neglect, which led him to develop a split personality. His inner child represents the innocent side, while his outer persona is driven by vengeance.
Overall, while the primary focus of Black Butler remains on Ciel and Sebastian's adventures, Alois plays a significant role as a complex antagonist, a character with unresolved trauma, and a plot device to add depth to the story and introduce further conflicts.