who does thor fight in the first movie
With his brother Loki.
Thor (film)
 As his brother Loki plots to take the Asgardian throne, Thor must prove himself worthy.
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Thor (film) [SEP] Introduction
As his brother Loki plots to take the Asgardian throne, Thor must prove himself worthy. Sam Raimi first developed the concept of a film adaptation based on "Thor" in 1991, but soon abandoned the project, leaving it in "development hell" for several years. During this time, the rights were picked up by various film studios until Marvel signed Mark Protosevich to develop the project in 2006, and planned to finance and release it through Paramount. Matthew Vaughn was assigned to direct the film for a tentative 2010 release. However, after Vaughn was released from his holding deal in 2008, Branagh was approached and the film's release was rescheduled to 2011.