Eivor is the name of the Viking warrior controlled by the player in Assassin's Creed Valhalla.
Eivor Varinsdottir is a Viking raider who leaves Norway with allies and establishes a settlement in ninth-century England. The character's story becomes entangled with the Hidden Ones, the Order of the Ancients, and the older Isu mythology that runs throughout the series.
Valhalla allows players to choose a male or female presentation for Eivor, or to let the game switch presentation according to the story. The name remains Eivor in each option. This flexibility is why references to Eivor can use different pronouns without indicating different protagonists.
Sigurd is Eivor's adoptive brother and a central character. Basim is a Hidden One encountered in the story, while Ragnar is a historical Viking figure referenced by the wider Viking setting. None of those names is the player character's name.