Who is the Norse god of thunder?

Thor, and he is Thursday - as Odin is Wednesday, Tyr is Tuesday and Frigg is Friday. Four days of the English week are named after Norse and Germanic gods, which survived the conversion to Christianity because nobody thought to change the calendar.

The written sources are a problem worth knowing about. Almost everything we have about Norse mythology was written down in thirteenth-century Iceland by Snorri Sturluson, a Christian politician recording material two centuries after conversion, partly as a handbook for poets who needed the old references to write in the traditional style. It is not scripture and was never intended as a coherent theology - so the tidiness of the modern retellings is largely Snorri's, and partly Wagner's.

Thor was also the popular god rather than the aristocratic one. Odin - god of poetry, war and cunning, who hangs himself on a tree for nine nights to gain the runes - attracted kings and poets; Thor, who defends the world by hitting things, attracted farmers, and hammer amulets are the commonest religious object found in Viking-age graves. They increase in number as Christianity spreads, which suggests people started wearing them as a statement rather than a habit.