In Egyptian mythology, Hatmehit, or Hatmehyt was a fish-goddess, originally a deification of the Nile, by the people in the area around Mendes.
In particular, it was the ba of Osiris, known as Banebjed (literally meaning Ba of the lord of the djed - referring to Osiris), that was said to have married Hatmehit.
As wife of Osiris, and mother of Horus, she eventually became identified as a form of Isis.
A living, sacred ram, was even kept at Mendes and worshipped as the incarnation of the god, and upon death, the rams were mummified and buried in a ram-specific necropolis.
In Mendes, they had considered Hatmehit, a local fish-goddess, as the most important god/goddess, and so when the cult of Osiris became more significant, Banebdjed was identified in Mendes as deriving his authority from being married to Hatmehit.
Later, when Horus became identified as the child of Osiris (in this form Horus is known as Harpocrates in greek and Har-pa-khered in Egyptian), Banebdjed was consequently said to be Horus' father, as Banebdjed is an aspect of Osiris.