Osiris

Osiris (also known as Wo-seer) was originally the God of Pharaohs until Set killed him. He later became the God of the Dead. He is the son of Geb and Nut and the husband of Isis and the father of Horus. He was born on the first Demon Day.

Background
Originally the sibling of Isis, Set, Nephthys, and Horus, he was later reborn to have Isis as his wife and Horus as his son. When Nephthys gave birth to Set's child, Anubis, she gave him to Osiris, claiming she did not want him to know his father. After Ra was tricked by Isis, Set, who couldn't stand the idea that Osiris was king, tricked Osiris and killed him. Horus and Isis were eventually able to avenge him and Osiris was revived as the Lord of the Dead.

The Red Pyramid
When Julius Kane summons him, Osiris is released with his sisters and brothers, Isis, Nephthys, Horus, and Set. He hosts Julius's body, but is promptly kidnapped by Set. Despite the efforts of Sadie and Carter Kane, Julius (as well as Osiris) die, but he is restored to his throne in the Land of the Dead.

Personality
Little is known of Osiris's personality, but he does seem to share Julius's body equally, allowing Julius to influence the Hall of Judgment and speak with his children.

Appearance
Prior to death, Osiris was described as a muscular, African man with hands strong enough to crush rocks. After his death while possessing Julius, he takes on Julius's appearance, but his skin is tinged a deep blue.

Powers and Abilities
Little is known about Osiris's powers, but they are implied to be great.

Osiris's symbol is literally his backbone, a symbol of great power, as said by Ruby Kane. Based on the fact that he is the god of the dead, he may possibly posess powers involving the dead, though that is unknown for sure.

Relationships
Isis: The two, formerly brother and sister, were reborn as a married couple. Isis loves her husband very much and is committed to helping him gain power.