Viggo plays the human soul tormented Aragorn also know as Strider. Aragorn is a very important role in the film, he is aire on Gondor and should noe, rightly be king but has straed from that path after freaing that he too will fall into the power of the ring and do what his for fathers did before him. Aragorn had been brought up by elve and had learnt to speak elvish at a very early age. He has fallen in love with Arwen and she too loves him back but their love is put on strain after Arwen is made to leave middle earth and follow the rest of the elves.
Aragorn, in the film had sworn to protect Frodo on his quest and so far he has kept to his pormise