Art and ceremonial maceheads (the tops of hammers used only for show) from the oldest part of Egyptian history show a strange animal that is made up of various other animals: dog, hyena, aardvark, donkey, jackal, and maybe even a pig or a giraffe. It has a long, Y-shaped tail and a strangely curving snout with no mouth and square ears. It's called a "sha," and it's the first symbol of Seth. Later on, Seth appears both as this funky fantastic creature and as a man with the Seth-beast's head. (Talk about old!)
Before Dynasty 1, parts of Egypt were divided between Team Horus the Younger and Team Seth. Eventually, Team Horus won (Horus always wins; it's just the way it is). But because Seth was respected, or maybe because everybody was still afraid of him, they called Egypt Tawy, or "Two Lands." The kings of Tawy, which was also called Kemet, or "the black land" (the name Egypt didn't come along until the Greeks, thousands of years later), wore the double crown. This crown was made by putting a white crown from Horus the Younger's southern Egyptian state on top of a red crown from Seth's northern Egyptian state, like Horus is wearing here.
We all know the story of how Horus the Younger wins the fight with his uncle Seth, and how after that, all the pharaohs of Egypt were named for him. At least two pharaohs in Dynasty 2 had problems with that idea, though. One, called Peribsen, or "Coming Forth by His (Seth's) Will," called himself the Living Seth instead of the Living Horus. Another called himself the "Living Horus and Seth," and his throne name was Khasekhemwy, or "Two Powers Appear, Shining in Glory." Their queens were called "She Who Sees Horus and Seth." Check it out.
The Hyksos (it's not a great name, it just means "foreigners") took over Egypt during the Second Intermediate Period. Because the Egyptian priests wanted them to honor local gods, they had to choose a god for themselves. Seth was an easy choice. He reminded them of their own storm god, Ba'al, and he also just happened to be the god of—you guessed it—foreigners. So the Hyksos gave Seth lots of attention and glory. As soon as the Egyptians kicked the Hyksos out, in Dynasty 17, they started getting rid of everything that the Hyksos had done. Because they couldn't actually get rid of a god, instead of asking Seth to leave, they just started talking about all the bad things he had done, like killing Osiris, or storming in the desert, or making friends with foreigners. Seth got blamed for everything, just like a redheaded stepchild. Only he wasn't a stepchild, though he was a redhead…
Ancient Egyptian armies were divided into divisions named for various gods. Under the Ramesside pharaohs, Seth became popular again since he was their family god – and the Seth Division fought very bravely in his name.
A pharaoh named Seti (literally, "the man of Seth") came to the throne and started a long period of Egypt's strongest empire. Most of his sons and successors were named Ramses, after his own father, who was the first of the 11 different Ramses kings. There were other kings, too, including another Seti and a Sethnakht ("Seth is strong.") They came from the Delta town of Avaris, where their family had been priests of Seth for centuries. Some of them, including the most famous one, Seti's son Ramses II, even had Seth's red hair.
Just like Team Horus the Younger won the Two Lands thousands of years earlier, the battle between Team Horus and Team Seth was still raging in the hearts and minds of Egyptians. Once the Ramesside kings were no longer on the throne, the powerful priesthoods of Horus the Younger, Isis, and Osiris made sure that everyone knew that Seth had done a terrible thing to Osiris and started to "punish" him by removing his image from temple walls and inscriptions and burying or breaking his statues in the shrines. In some places, like Karnak, only a few images of Seth remain, in the hieroglyphs of Seti's name that are too high up on the ceiling of the hypostyle hall for anybody to scratch out. In other places, like the temple of Kom Ombo, Set's son Sobek takes his place. In other places, Anubis or Thoth appear in Seth's place.
Meanwhile, Egyptians who lived in the desert still honored the Red Lord. In the Kharga Oasis, south and west of the Nile in Egypt's so-called Libyan Desert, Seth had a shrine of his own at the temple of Hibis, where people came to ask the "Lord of the Oasis" to tell their future. (We wonder how many times he gave bad fortunes just to see the looks on their faces) Seth also appears in Hibis temple with his brother, Horus the Elder. Together, they are shown as a fierce falcon-headed god (or a god with two heads: one falcon, one Seth-beast) called Bawy, or Two Powers. Eat your heart out, Horus the Younger!
Unfortunately, the Persians were foreigners again, and foreigners ruined Seth's reputation for good. Roman writers like Plutarch equated Seth, the "evil" murderer of Osiris, with Typhon, a Greek monster associated with chaos and destruction. Even though thousands of years of Egyptian mythology show that Seth isn't the serpent of chaos (which the Egyptians named Apep or Apophis), but the last line of defense against Apophis, it was easy to make Seth all bad all the time. Thousands of years of Seth's being erased from temples and inscriptions in Egypt didn't help, and so Seth was equated with Apophis and other demons. Centuries later, he'd eventually be equated with the Christian Satan. Yowza.