Short answers, pulled from the story.
Ra was the ancient Egyptian deity of the Sun, god of order, kings, and the sky. By the Fifth Dynasty, in the 25th and 24th centuries BC, he had become one of the most important gods, identified primarily with the noon-day Sun and believed to have ruled as the first pharaoh of Egypt.
Each night Ra descended into the Duat, the underworld of twelve hours, traveling on the Mesektet Barque in his ram-headed form. He sailed the subterrestrial Nile through twelve gates and regions, faced an attack by the serpent Apophis, and returned at dawn to light the day.
The Egyptians called themselves the "Cattle of Ra" because, in some accounts, humans were created from Ra's tears and sweat. Ra was believed to have created all forms of life by calling them into existence with their secret names.
The chief cultic center of Ra was Iunu, "the Place of Pillars," later known as Heliopolis or "Sun City," today located in the suburbs of Cairo. There Ra was identified with the local sun god Atum, and the Mnevis bull, an embodiment of Ra, was also centered at Heliopolis.
Ra was merged with Horus as Ra-Horakhty, "Ra, who is Horus of the Two Horizons," and fused with Amun as Amun-Ra during the New Kingdom. Amun-Ra was given the title "King of the Gods," and Ra also combined with Atum as Atum-Ra and with Montu as Montu-Ra.
Apophis, also called Apep, was the god of chaos, or isfet, and Ra's arch-enemy. He was an enormous serpent who tried to stop the sun-boat's journey every night by consuming it or halting it with a hypnotic stare, and was said to lie just below the horizon line.
The worship of Ra ended with the rise of Christianity in the Roman Empire. His cult had grown from roughly the Second Dynasty and peaked when he became a state-deity in the Fifth Dynasty.