In battle, Space Marine Librarians protect the Chapter from the psychic abominations of the enemy by keeping vigil against daemonic attack. They direct their own unearthly powers against the enemy and unleash bolts of warp energy to rend and incinerate their foes. Sometimes, they conjure horrors that freeze the mind and goad even the sturdiest warriors into flight.

You may include a Librarian in your Dark Angels army as an HQ choice.