In Honkai Impact 3rd, he inherited the name "Welt" and the Herrscher's core from Welt Joyce, the first Herrscher of Reason, when he died in 1955. Later, he became the sovereign of Anti-Entropy and saved Earth from annihilation time and time again.

Spoiler

After an incident with the Sky People in 2029, Welt has noticed their interest in Honkai: Star Rail's Murata Himeko, his former student, and felt obligated to protect her as a teacher who failed to do so once. As a matter of coincidence, that Himeko happened to stumble across the dead spaceship and take Welt Yang and his companion across the Astral Express as passengers.

In Honkai: Star Rail, he's an animator by trade and a seasoned member of the Astral Express Crew.