I was browsing Wikipedia and came upon three different variations for Ra's origins:
- In the former version, a mound arises from the waters. An egg was laid upon this mound by a celestial bird. The egg contained Ra. In some variants, the egg is laid by a cosmic goose. However, the egg was also said to have been a gift from Thoth, and laid by an ibis, the bird with which he was associated.
- Later, when Atum had become assimilated into Ra as Atum-Ra, the belief that Atum emerged from a (blue) lotus bud, in the Ennead cosmogony, was adopted and attached to Ra. The lotus was said to have arisen from the waters after the explosive interaction as a bud, which floated on the surface, and slowly opened its petals to reveal the beetle, Khepri, inside. Khepri, an aspect of Ra representing the rising sun, immediately turns into a weeping boy – Nefertum, whose tears form the creatures of the earth.
Source: Ogdoad: In Egyptian mythology
- Ptah is rarely mentioned in the literature of Old Kingdom pyramids. This is believed by some to be a result of the Ra-worshipping people of Heliopolis being the main writers of these inscriptions. Followers of Ra were known to be jealous of Ptah. While some believed that Ra is self-created, others believed that Ptah created him.
Source: Ra: Rival gods
Given Ra's popularity and central position in Egyptian mythology, I would have assumed his origin story would be somewhat standardized. Local variations are to be expected, of course, but I couldn't find any information on which one stood out - if any.