Utagawa School of Ukiyo-e

Woodblock printing in Japan is a best known for its use in the ukiyo-e artistic genre of single sheets. The Utagawa school (歌川派) was a group of Japanese woodblock print artists, founded by Toyoharu. His pupil, Toyokuni I, took over after Toyoharu's death and raised the group to become the most famous and powerful woodblock print school for the remainder of the 19th century.
Hiroshige, Kunisada, Kuniyoshi, and Yoshitoshi were Utagawa students. The school became so successful and well known that today more than half of all surviving ukiyo-e prints are from it.
Founder Toyoharu adopted Western-style deep perspective, an innovation in Japanese art. His immediate followers, Utagawa Toyohiro and Utagawa Toyokuni adopted bolder, more sensuous styles than Toyoharu and specialized in different genres — Toyohiro in landscapes and Toyokuni in kabuki actor prints. Later artists in the school specialized in other genres, such as warrior prints and mythic parodies.
It was a Japanese custom for successful apprentices to take the names of their masters. In the main Utagawa school, there was a hierarchy of gō (art-names), from the most senior to junior. As each senior person died, the others would move up a step.
The head of the school generally used the gō (and signed his prints) as Toyokuni. When Kunisada I proclaimed himself head of the school (c. 1842), he started signing as Toyokuni, and the next most senior member, Kochoro (a name also previously used by Kunisada I, but not as his chief gō), started signing as Kunisada (Kunisada II, in this case).
The next most senior member after him, in turn, began signing as Kunimasa (Kunimasa IV, in this case), which had been Kochoro's gō before he became Kunisada II. (The original Kunimasa I had been a student of Toyokuni I.)