Yama is the god of death and a technological whiz kid. He's a genius, although his genius is less the kind that makes for a debate team captain and more the kind that creates machines with some serious death dealing capabilities. He's also perhaps the most powerful god currently running amok in the Celestial City.
But what's death incarnate like anyway? Well, believe it or not, he's a lot like a teenager.
Death is a young god. According to Jan, he's a third generation "snot-nosed brat of dubious parentage" that once "anesthetized one of everything that moves out there and dissected it, taking such pleasure in his studies that we called him deathgod" (2.178). Unfortunately, while working on a generator, there was an accident, and Yama was transferred into an adult body at the tender age of sixteen.
So we have a character that is highly knowledgeable, trapped in a man's body, has all the emotional growth of a teenager, and is given the job of death god. What can possibly go wrong?
Ironically, the god of death's story is very much a tale about life. Yama begins the story a hotheaded pup out to prove himself to the woman he loves, Kali—Sam need only insult her to have the super-intelligent Yama walk right into his quicksand trap. Ah, youth and the vitality of young hearts.
Speaking of Sam, he serves as a type of teacher to Yama, discussing twice with the young god his place within the pantheon and why he desires to grant his services to the gods (4.557). Then Yama and Kali get married, but the honeymoon period doesn't last long as Kali agrees to give up being Kali to replace the murdered Brahma. Yama seeks out Sam and fights on his side to seek revenge on the woman he love/hates. How quickly young love fades, right? But in the end, Yama takes a mentally damaged Kali as his daughter, naming her Murga (7.572).
See the pattern? Through the course of the novel, Yama goes from boyhood, to manhood, to marriage, to love lost, and ends with fatherhood. Although already highly intelligent and in the body of a man, Yama must grow as a person and come into his own just like the rest of us would on the mere mortal track of life. In other words, even the god of death can't skip over life.
At the novel's end, Yama goes to join Sam wherever he has gone. Whether as a companion or student, we can't say.
Yama is the god of death, obviously. But let's not assume Yama is simply the Grim Reaper of Hinduism and let that be that. Yama rules over the Southern region of the world in a palace called Kalichi, and unlike the Grim Reaper—who does all his own leg work—Yama is more of the administrative type.
Yama's attendants register the life of every human in the Book of Destiny, and when a person's time ends, Yama sends his people to Earth to bring the doomed soul to Kalichi for judgment, kicking and screaming if they must. Last we checked, the Grim Reaper would never miss an opportunity to collect a body himself.