Legend has it that a Christian can kill a troll if they say its name aloud, so as you can imagine troll names are some of the best-kept secrets in the world. Despite that, the names of some trolls from literature and Norse Mythology are known:
Grendel – the troll from Beowulf and one of the three main antagonists of the epic poem
Dunker – a troll mentioned in an old folktale from Fosen
Ymer – a jötunn and the largest creature from Norse Mythology
Dovregubben – the troll king in Henrik Ibsen’s Peer Gynt
Hrungnir – a jötunn and the largest of its kind in Old Norse texts
Trym – king of the jötnar, reigned in Jötunheimr
Geirröd – another jötunn from Norse mythology, father to Gjálp and Greip
Mark Bere Peterson’s Hauntings, Urban Legends, Paganism & Witchcraft 