Arngeir

Arngeir is a powerful Greybeard elder who serves as instructor and mentor in the Way of the Voice for Dragonborns. He and his fellow Greybeards stay at High Hrothgar.

Interactions
After the Dragonborn retrieves the Horn of Jorgun Windcaller he can be asked where to find a Word of Power by asking "Have you located any Words of Power?" Then, a location will be added to the map and a miscellaneous objective will be added to the journal. If the Dragonborn decides to kill Paarthurnax for the Blades he refuses to speak to the Dragonborn.

Behind the scenes

 * He is voiced by Christopher Plummer.

Trivia
It is assumed that Arngeir is the only Greybeard (Other then Paarthurnax) that can speak both Human and Dragon. Evidence of this is Einarth yells or shouts at Arngeir in Dragon, during The Throat Of The World quest, telling him to help the Dragonborn. No other Greybeard responds to you in elaborate speech besides Arngeir and Paarthurnax. If asked why none of the other Grey Beards speak, he says that their voices are too powerful and that they can kill with but a word, meaning that Arngeir could be the least powerful. This is unlikely however since he's seen as a de-facto leader of the Greybears in Parthanax's place. Also, Parthanax can speak both in the Dovah tongue, and human language, without doing much harm to his surroundings.