Gyudon is a bowl of rice topped with sliced beef and onion which are simmered with soy sauce and sugar. The dish was made by putting the ingredients of sukiyaki, also called gyunabe, which is Japanese style stew which simmer sliced beef and vegetables in a shallow pot. Gyudon was first made and named by Eikichi Yoshida who founded Yoshinoya in 1899.
It is known that sukiyaki has Kanto style is based with fermented soy bean paste, and Kansai style is based with soy sauce. In Kanto region (eastern part of Japan), gyudon was first seasoned with fermented soy bean paste, just like sukiyaki, to reduce the smell of the meat. The Kanto style gyudon first simmer the meat with stock mixed with seasonings, which is the reminiscent of sukiyaki.
On the other hand, in the Kansai region (western part of Japan), the Kanto style gyudon did not become popular. Instead, in the Kansai region, simple soy sauce based gyudon became popular, since fresh meat such as local Kobe beef was easy to obtain. The Kansai style gyudon first fry meat, season with sugar, soy sauce, and sake, and then put the other ingredients such as onion.
When the Kanto earthquake occurred in 1923, Tokyo suffered from devastating damage, and many gyunabe and gyudon restaurants had to close. After the city restored from the damage, Kansai style soy sauce based gyudon was brought to Toyko and it became the main stream gyudon.
Sukiyaki-don is also considered as one kind of gyudon, which contains string konnyaku, roasted tofu, and green onion. However, regular gyudon still only use beef and onion. Pickled onion, mix of seven spices, raw egg will be added as the way customer prefers.