Atum, sometimes rendered as Atem or Tem, is an important deity

Deity

A deity is a recognized preternatural or supernatural immortal being, who may be thought of as holy, divine, or sacred, held in high regard, and respected by believers....

 in Egyptian mythology

Egyptian mythology

Ancient Egyptian religion was a complex system of polytheistic beliefs and rituals which were an integral part of ancient Egyptian society. It centered on the Egyptians' interaction with a multitude of deities who were believed to be present in, and in control of, the forces and elements of nature...

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Atum's name is thought to be derived from the word 'tem' which means to complete or finish. Thus he has been interpreted as being the 'complete one' and also the finisher of the world, which he returns to watery chaos at the end of the creative cycle. As creator he was seen as the underlying substance of the world, the deities and all things being made of his flesh or alternatively being his ka.
Atum is one of the most important and frequently mentioned deities from earliest times, as evidenced by his prominence in the Pyramid Texts

Pyramid Texts

The Pyramid Texts are a collection of ancient Egyptian religious texts from the time of the Old Kingdom. The pyramid texts are possibly the oldest known religious texts in the world. Written in Old Egyptian, the pyramid texts were carved on the walls and sarcophagi of the pyramids at Saqqara during...

, where he is portrayed as both a creator and father to the king.