How to get Gravedigger - Elder Scrolls: Morrowind
Location: Mournhold, Throne Room
Requirements: Not required but recommended you finish Tribunal Story as this NPC plays a primary role in it
Video: How to get Gravedigger in Morrowind
Gravedigger is a unique weapon added into the game during the Tribunal Expansion Pack. This weapon is carried around by Tienius Delitian who is found in the Royal Palace Throne room in the city of Mournhold. In order to obtain this weapon from Tienius you'll need to kill him. Unless you want the entire Throne Room to attack you when you fight Tienius you'll want to use Frenzy Humanoid on him or Taunt to get him to attack you. I recommend also pulling him into a corner or by one of the doors leading in/out of the room to prevent anyone else being hit by any attacks.
How to Reach Tienius: Once in Mournhold use Divine Intervention to be taken to the Royal Palace Courtyard. Turn around and go through the door to Royal Palace: Imperial Cult Services and then through the door to Royal Palace: Throne Room.
It's recommended that you wait until you've completed the Tribunal Story Quests before you kill Tienius since he's a required NPC in many of the quests for this Expansion Pack. Alternatively, if you don't plan to do any of Tribunal with this character then it doesn't matter when you kill him.