I am not sure of this character/lore. First off the human religion in Alagaësia needs to be better defined.
As for the book according to the IC wiki:
Unulukuna, sometimes known as the "Old One", was one of the deities worshipped by the Wandering Tribes. It is not known what Unulukuna is the god of, but according to Fadawar, Unulukuna specified how a family should live and how an individual should divide their loyalty. According to Nasuada in Inheritance, Unulukuna was the creator of all the deities worshipped by the Wandering Tribes. She also stated that Unulukuna offered life everlasting.
Behind the scenes
Unulukuna was probably named and modeled after Unkulunkulu, the creator god for the Zulu people of South Africa. Both are also considered the ancestor of all men who taught them everything there is to know about life.