According to the World of Warcraft wiki: Medivh was the last Guardian of Tirisfal, an ancient line of protectors bestowed with great powers to do battle with the agents of the Burning Legion. He was corrupted even before birth, and possessed by the spirit of the demonlord Sargeras who used Medivh in his plan to conquer Azeroth. Medivh contacted the orcish warlock, Gul'dan, and together they opened the Dark Portal, which allowed the Burning Legion to begin its destruction of Azeroth. He was slain shortly after by a party led by one of his friends, Lothar.
Ben Foster had this to say about his character:
"The character in Warcraft that I play is named Medivh. He's a mage, which is essentially a sorcerer. He came up in a time protecting an area, and the way he protected this area was through magic. As peace returned to this land he took a break. He hung up his staff, so to speak, or let his guns get dusty. We meet him as his friends are returning asking for his help in a battle. What's exciting about Duncan Jones' take on this video game is that it shows both sides of the war. It shows both sides of a conflict, which is exciting to me. It's not just a video game turned into a movie. It's asking, hopefully, an important question of, where do we limit our compassion for what we consider to be the bad guys?"
Ben Foster will not be playing a CGI or Motion Capture character in the film, though he goes onto praise VFX house ILM for their genre defying work. Asked if he was required to wear a Mo-Cap suit on set, Ben Foster replied,
"No, mine's not [motion capture], but there are interactions with a lot of characters that are. There are a lot of different kinds of creatures in this picture that I interact with. The way that they're pushing motion-capture -- I just saw some of the test footage -- it's unlike anything I've ever seen. It's performance-capture. It pushes it to the next level. It's going to be one helluva 3D event."
Warcraft comes to theaters March 11th, 2016 and stars Paula Patton, Anson Mount, Paul Dano, Colin Farrell, Travis Fimmel, Anton Yelchin, Ben Foster, Toby Kebbell. The film is directed by Duncan Jones.