In Egyptian mythology, Apophis/Apep was the serpent-like dragon, most often depicted as a hooded cobra, that daily attempts to catch and destroy the sun god Ra.
Apep was an evil god, the deification of darkness and chaos and thus opponent of light and Ma'at (order/truth), whose existence was believed from the 8th Dynasty.
Apep formed part of the more complex cosmic system resulting from the identification of Ra as Atum, i.e. the creation of Atum-Ra, and the subsequent merging of the Ogdoad and Ennead systems.
Consequently, since Atum-Ra, who was later referred to simply as Ra, was the solar deity, bringer of light, and thus the upholder of Ma'at, Apep was viewed as the greatest enemy of Ra, and thus was given the title Enemy of Ra. As the personification of all that was evil, Apep was seen as a giant snake/serpent, or occasionally as a dragon in later years, leading to such titles as Serpent from the Nile and Evil Lizard.
Though because of his size considered to be a 'python' by some Egyptologists, this identification does not square with texts that mention Apeps 'poison' and never mention an act of strangling.