There were two completely different gods, both called Hapy.
The first Hapy is one of the four children of Horus. Like the other children he had the task to protect part of the internal organs of the deceased, which were removed from the body during mummification and which were stored in four so-called canopic jars. Hapy was especially in charge of the protection of the lungs, and spells inform us that he himself was helped or protected during this task by the goddess Nephthys.
Hapy is depicted as a man or as a man with a baboon’s head. The canopic jar containing the lungs usually has a lid showing the head of Hapy.
The second Hapy is the god of the Nile inundation, usually depicted as a fat man with pendulous breasts, which is a sign of fertility and abundance. He can be seen in the bottom register on the walls of many temples, where processions of gods, personifying the nomes of Egypt and carrying the products of Egypt as offerings, are all in the form of Hapy, with the emblem plants of Upper- and Lower Egypt on their heads.
There were other gods who were associated with the Nile and the inundation, especially Osiris (whose body, according to myth, was thrown into the Nile and whose resurrection was associated with the rising of the water) and Sobek (the crocodile god who lived in the Nile), which explains why the cult of Hapy was relatively unimportant in Egypt.
Hapy was especially venerated in Aswan and Silsila, places near the first cataract were the source of the Nile was believed to be.