Serapis

Serapis was a Greco-Egyptian god worshipped in ancient Egypt.

The god was introduced by Ptolemy I Soter, the founder of the of Egypt, who sought to accomodate the similar beliefs of both Greek and Egyptian culture. To this end, he amalgamating the names of Osiris and Apis, forming the name Serapis.

By the 1st century BCE, the cult of Serapis was widespread across Egypt, with various towns and cities containing a temple or shrine dedicated to him, the most notable being the Serapeum of Alexandria.

Reference

 * Assassin's Creed: Origins