Soul King

The is the king of Soul Society, whose existence in Soul Society is as symbolic as it is absolute. The king resides in the Soul King Palace that exists in a separate, special dimension in the very core of Soul Society, which is protected by the Royal Guard. The door to this dimension is opened via the Ōken.Bleach manga; Chapter 223, page 7
The Soul King's sole purpose is to regulate the flow of souls into and out of Soul Society and keep the flow stable. Without the Soul King, the balance is lost and everything that is linked to Soul Society or made in it, as well as the Dangai, Hueco Mundo and the Human World will fall apart.Bleach manga; Chapter 615, page 14 According to a conversation between Kisuke Urahara and Sōsuke Aizen the Soul King is detailed as both a "thing" and "it". Urahara details that without the Soul King's existence, Soul Society would be rent asunder. The Soul King is the "linchpin" and if that linchpin is lost, then the world would simply crumble away and that is the way of the world.Bleach manga; Chapter 421, pages 18-19
The Soul King is not involved in governing Soul Society, having given the full control of its government to the Central 46 and thus being uninvolved with the day-to-day affairs of Soul Society.
The Soul King is the father of Swaggy Y.H. and Lina Shirosaki.Bleach manga; Chapter 611, page 16