Njord

Njord (pronounced "NYORD"; often spelled Njörðr) was the Norse Vanir god of seas, wealth, wind, fire and fishing. He was the father of Frey and Freya and the grandfather to both Blitzen and Magnus Chase.

The Sword of Summer
Njord was mentioned several times throughout The Sword of Summer, with Ran being able to detect that Magnus Chase is his grandson.

Trivia

 * His Greco-Roman equivalent is Poseidon/Neptune.
 * He was briefly married to Skaidi, the Norse goddess of Winter.
 * It is theorized that Nerthus, the Vanir goddess of the earth, harvest and revenge is his sister and mother of his twin children.