It’s pretty well known that Buddhism started in India, but eventually became much more popular in eastern Asia. Also, while Siddhartha Gautama apparently started Buddhism as an alternative to Hinduism, it came to take on many aspects of the earlier religion. And as it spread into other nations, it was merged with some of their local mythology as well. This seems to be the most likely explanation for the proliferation of Yama, originally introduced in Hinduism as the god of death.
In imagery, he rode around on a buffalo, carrying a mace in one hand and a noose in the other. He would use these implements to remove the soul from a person’s body at its allotted time of death. He then takes the spirit to one of the many hells, or back to Earth for rebirth.
In China, Yama is known by the name Yen-Lo-Wang, and there appears to be a bit of mythology that said he was originally considered too lenient. Because of this, he was demoted from ruler of all the hells to merely the one in charge of the fifth court in particular.
In this position, his specialty is gouging and boiling. Sounds like a blast. He’s also a bureaucrat, keeping a filing system telling the death dates of everyone on Earth. There’s a mention on Wikipedia that Yen-Lo-Wang was sometimes considered a position rather than an individual, and that there were different lords of the Fifth Court of Hell. Could be, I suppose. I understand that he also appears in the famous Chinese novel Journey to the West, in which the main character Sun Wukong (better known as simply “Monkey”) sabotages Yen-Lo-Wang’s records to make himself and his fellow monkeys immortal. Also, as an Internet search for the name reveals, Yen-Lo-Wang is a mech in BattleTech. Oh, franchises featuring giant robots, is there any any mythology you won’t reference? Not that that’s a bad thing, mind you.