The oldest god was the Sun god, Re. During the Old Kingdom, kings built their pyramids to worship Re. But each region also had its own gods. For example, the main god of Thebes was Amun. So when the capital of Egypt moved to Thebes, Amun became more important.
As time went by, the pharaoh and the priests felt it was important to have a god that looked after the common people. This was Osiris and, as a result, Osiris became a more important god.
Egyptians had paintings and sculptures that represented the gods, but they did not worship these objects. They were simply thought of as a place which the god might inhabit for a while.