A professional from 2004 until 2008, he was the last WEC Heavyweight Champion before it was abolished when Zuffa purchased the organization.
Olsen made his debut against Craig Zellner on March 17, 2005 at WEC 14: Vengeance.
He defeated Johnson via submission due to a knee injury and became the new heavyweight champion.
[3] Olsen made a title defense against Mike Kyle on May 5, 2006 at WEC 20: Cinco de Mayhem.
Kyle was disqualified after hitting Olsen with illegal strikes, for which he was placed on the national suspension list by CSAC.