In the Marvel Comics Universe, Thanos is a big, mean, purple super villain who is totally in love with Death. (Guess where his name came from?)
Thanatos was the name of an awesome arcade game from the 80s where you got to be a dragon and fly around burning stuff. If anyone can get their hands on it, please share the love.
There is an extremely hardcore Dutch death metal band called Thanatos.
Sigmund Freud had this idea that everybody has a thing called a "death drive" which leads them to do self-destructive stuff. Later psychologists started calling this urge Thanatos.