Hiccup and Toothless are brothers, but don't really look the part. They look completely different, but with Toothless' being a Night Fury, it makes sense
Hiccup and Valka were stolen by dragons during a raid. They lived with them for 20 years, and learned to trust them. Toothless and Hiccup bonded like brothers, and flew around the world at night, riding the winds of the twilight.
Then, when they meet a girl named Astrid and a dragon named Sky, their world is forever changed.... but when Toothless looses Sky, his life is forever changed a bit more....
P.s. Dreamworks own all characters, with the exception of a few I made up (You'll know when you find them...)