Lethias Enaril is an undead spirit and former elven bladesinger.
Location[]
He stands in the central corridor in front of the collapsed entrance to Sehanine Tower (weapons tower) on level 4 of the Severed Hand.
Background[]
Long ago, he was an elite elven warrior protecting the Hand of the Seldarine, which gained him the title "Bladesinger of the Seldarine".
When the Hand fell to the orc and goblin hordes, Lethias carried out a suicide mission by leading scores of the enemy into Sehanine Tower, which the elves had rigged to self-destruct. The tower exploded as planned, with Lethias and many orcs and goblins inside it.
But unexpectedly, he returned as an undead creature, together with many other fallen soldiers on both sides. Unlike most of the others, he has retained his mind and even recognizes that he is undead now. 
Interaction[]
When you first talk to him, he interrogates you about your reasons for being here.
If you either threaten him or state your intention to loot treasure, he turns hostile and attacks you.
Otherwise, you can ask him about his backstory and about Larrel.