Stefen joined the computer graphics department at Industrial Light & Magic in 1990 to work on Terminator 2: Judgment Day.  During his 15 ½ years at ILM, he worked on numerous projects that represent significant mile-stones in visual effects history.  

In 1997, Stefen received a British Academy Award (BAFTA) for his visual effects supervision on Twister and again in 1998 for Saving Private Ryan.  He won a third BAFTA for The Perfect Storm in 2000.  He also received Academy Awards nominations for his work on Twister, The Perfect Storm as well as Master and Commander.

In addition to his visual effect supervision duties, Stefen worked as the second unit director on Galaxy Quest in 1998 and Dreamcatcher in 2002.

In 2005, he ventured into feature-film directing with Eragon, which grossed over $250 million in worldwide box office returns upon its release at the end of 2006. The film is an action-adventure fantasy with a budget of $96 million and was produced by 20th Century Fox. 

After directing Eragon, Stefen has been working as an independent Visual Effects Supervisor on a wide range of projects the most notable of which is certainly his work on Game of Thrones. 

Prior to joining ILM, Stefen served as director of production at Mental Images in Berlin, as well as working as a scientific visualization program manager at the National Center for Supercomputing Application at the University of Illinois. His first job in the computer graphics industry was position of technical director at Digital Productions in Los Angeles in 1985.

Stefen graduated from a California State University with a computer science degree in 1984.