Apep

In Egyptian mythology, Apep (also spelled Apepi, and Aapep, or Apophis in Greek) was an evil demon, the deification of darkness and chaos (isfet in Egyptian), and thus opponent of light and Ma'at (order/truth), whose existence was believed from the Middle Kingdom onwards. His name is reconstructed by Egyptologists as * because of written 3pp(y), surviving into later Coptic as Aphōph.
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[Egyptian] An Egyptian monster living in perpetual darkness. This snake god is the chief of the antagonists of the sun god Re and each night he tries to stop the sun god's barque on his journey through the underworld. In the struggle between light and darkness, the monster is wounded by the divine entourage of Re with knives and spears. The god Seth and the god Mehen were often depicted defending the solar barque. Apep is the personification of darkness, evil, and chaos. Occasionally, the battle was decided in his favor, causing a solar eclipse, but his victories were of short duration for Re always triumphed in the end. Eventually, Apep was slain by Re, who cut up his body and burned it. The Greeks referred to him as Apophis.

Apana (Sanskrit) [from apa away, off, down + an to blow, breathe] Down-breath; one of the vital airs, life-currents, or pranas which vitalize, build, and sustain the human or animal body. As apa indicates, it is the prana which ejects from the system material which it no longer requires, such as wastes, etc. Opposite in function to the upward-tending breath, udana.

Apap or Apep (Egyptian) Apophis (Greek) The serpent of evil, generally denoting matter in its lower reaches of differentiation from spirit; the slayer of every soul too loosely linked to its immortal spirit. Typhon, having slain Osiris, incarnates in Apap and seeks to kill Horus (the personal ego), but is slain by Horus through the power of Horus' father Osiris, the buddhic principle. It is also the serpent which is slain by the sun god Ra. The combat is another aspect of the myth of the battle between Horus and Set, these deities representing cosmic and physical light and cosmic and physical darkness respectively. "Apap is called 'the devourer of the Souls,' and truly, since Apap symbolizes the animal body, as matter left soulless and to itself. Osiris, being, like all the other Solar gods, a type of the Higher Ego (Christos), Horus (his son) is the lower Manas or the personal Ego. On many a monument one can see Horus, helped by a number of dog-headed gods armed with crosses and spears, killing Apap" (TG 26).
The same general story is found in St. George and the Dragon, Michael and Satan, etc. Apap, the serpent of evil, is slain by Aker, Set's serpent, showing the twofold meaning of the serpent symbol. Cosmologically this means the bringing into order of the confused and turbulent principles in chaos; in the human being it refers to the trials of initiation; in astronomy, to eclipses.