|A depiction of the Nun (Nu), the 150-day Nile River annual flood, Nu's ark, to Ma-Nu and the flood, to Noah (Nuh) and Noah’s ark conceptual evolution.|
Heliopolis creation myth of a land mound arising following the original flood a theory based on the annual 150-flood cycle of the Nile river, at the end of which a fertile black soil called keme (pronounced 'chem') is left behind in the receding water. Hence, similar to the observed flood cycle of the Nile, it was hypothesized that there was one great primordial flood out of which a land mound arose, out of which the sun was born.
This soon became known as the Ennead cosmogony (group of nine) or the Heliopolitan Ennead, in which Nun is perceived as transcendent at the point of creation alongside Atum the creator god, who then self-creates two progeny gods: Shu (air) and Tefnut (moisture), who then create two progeny gods: Geb (earth) and Nut (heaven), who then create four progeny gods: the 'good' pair Osiris and Isis and the 'bad' pair Seth and Nephthys: 
The following is an etching (Ѻ) of is Nu carrying the solar barque, containing Ra in the form of Kephri (Ra-Kephri), i.e. the sun disc, as it sails through the day sky, as found on a temple wall in Abydos, Egypt: (Ѻ)
Father of Ra
The name of this sun or sun god came to be known as Ra, the son of Nun. Ra eventually came to be seen as the original progenitor of all life, hence the "father" to all humans, where after the full name of Ra was written in Hieroglyphics as:
Father Ra son of Nun (e.g. father Tom son of Steve)
In the sense that the prefix Ab- or B- meant "father" and the suffix -ham or -hma, meaning keme (or black land), pronounced chem or ham, the name Father Ra son of Nun became rewritten in the B-ra-hma-ic theologies (20% of modern religions) and Ab-ra-ham-ic theologies (53% of modern religions) as:
although the original Egyptian association became lost or discarded through syncretism, although not enough to have covered up the overlap in stories of the latter two versions of the character (sister-wife issue, sacrifice of son faith test, Ma-Nu/Noah flood forefather, etc.)
In the scheme of the Hermopolitan Ogdoad (Hermopolis, 2400BC) theory, Nun was coupled to the primordial goddess Naunet, the pair epitomizing the primordial abyss, and Ra became a syncretism with the fire god Atum, called Re-Atum.
Noah | Ma-Nu
The primordial flood-then-land aspect of Nun became reformulated in the Hindu-Buddha version as the flood god Ma-Nu. The primordial flood-then-land aspect of Nun became reformulated in in later Judea-Christian-Islam version as a man named Noah, a person who built an ark before the flood and landed on a mound after the flood, releasing three birds, at 40-day intervals, on the third day of which (120-days) the sun rose (just as in the original Egyptian version a bird burst forth from the land mound Nun carrying the sun on its head into the sky; later recorded by Herodotus as the phoenix).
1. (a) Budge, Wallis. (1904). The Gods of the Egyptians, Volume One (pg. 78). Dover, 1969.
(b) List of Egyptian hieroglyphs – Wikipedia.
(b) Jordan, Michael. (1993). Encyclopedia of Gods. Facts on File.
2. Thims, Libb. (2003). Human Thermodynamics, Volume 3. Unpublished manuscript. IoHT publications.
3. Ennead – Wikipedia.
● Nu (mythology) – Wikipedia.