According to the Prose Edda, also known as Saemund's (Sigmund's) Edda; Thor was to meet his death during the battle of Ragnarök. It was the great "World snake", Jörmungandr who was to be his undoing. The two, being of roughly even match, engaged one another upon the outset of the battle and remained locked in combat until Thor dealt a death blow to the great serpent. He was only to take nine steps, however, before falling dead from the venom. It is variously disputed that Thor was not actually poisoned by the serpents venom, but that he was drowned in the torrent of it that gushed from the dying creatures fangs. The interpretation is, of course, all in the word "Drowned". It could be that Thor was drowned bodily (in a literal sense) or it could, more metaphorically mean that he was "drowned from within" (overcome by toxins). In order for the reader to decide upon the appropriate translation for themself, here is that particular verse... Odin's son goes / With the monster to fight; / Midgard's Veor in his rage / Will slay the worm; / Nine feet will go / Fiorgyn's son / Bowed by the serpent / Who knew no foe.
Thor Bjørklund died in 1975.
Thor Henning died in 1967.
Thor Lund died in 1999.
Thor Myklebust died in 1989.
Thor Johnson died in 1975.
Thor Jensen died in 1976.
Thor Ørvig died in 1965.
Thor Knudsen died in 2006.
Thor Fossum died in 1993.
Thor Lange died in 1915.
Thor Gystad died in 2007.
Thor Vilhjálmsson died in 2011.