Arcturus is Algol's son. Jealous of his father's power, he stole Soul Edge. However, his will was not strong like his father's, and he was possessed by the evil sword. It then commanded him to destroy his father. Having no other choice, Algol overwhelms and kills his son in combat. Algol's sorrow after the death persuades him to create the spirit sword Soul Calibur.
In Soulcalibur IV
Arcturus is seen three times in the game: In one of Algol's flashbacks; in Talim's ,Sophitia's ending; and as an illusion created out of his memories by Zasalamel, sent to fight Algol in his story. The illusory Arcturus uses Nightmare's fighting style and wields Soul Edge (Nauplius). He is the only NPC in the game to do so.
He cannot be created in Character Creation; much of his costume was designed to look similar to Algol's, whose clothing cannot be selected, but his hair style can be selected aswell as his weapon Soul Edge (Nauplius) for Nightmare however his face & hairstyle can be used in Character Creation mode.