He has worked on the films of George Lucas, Steven Spielberg, and James Cameron, among others, and has won nine Oscars in total: eight for Best Visual Effects and a Technical Achievement Academy Award.

"[2] He has been identified as "a pioneer in bringing a new wave of visual effects films to the public, opening the doors for screenwriters and directors to tell stories never before possible with a new realism through the use of his skills in cinematic arts and advanced technologies.

[6] He never attended film school but was self-taught, and also learned through friendships with other young Los Angeles effects enthusiasts, including Jim Danforth and David Allen.

In 1976, Muren was hired as 2nd cameraman at Industrial Light & Magic (ILM), then an upstart visual effects studio founded by George Lucas,[10] to work on Star Wars.

[6] In their first big project, Muren directed the Division in creating shape-shifting animals using in-house custom software for "morphing" (blending) footage of animatronic models in Willow (1988).

[13] Steven Spielberg had intended to use go-motion for the Jurassic Park dinosaurs, but a CG test of a walking skeleton T-Rex made by ILM's Steve Williams and Mark Dippe (with Marin County as the backdrop) convinced Universal to fund a proof-of-concept, photo-real, no-excuse shot.

[4] In three months, following Muren's cinematic goals, the ILM CG department broke new ground, adding organically moving flesh and muscle to the creature's skeleton, covering it with animal-like skin texture and exterior sun and bounce lighting to make a photorealistic walking T-Rex.

Due to their similarity in facial appearance (despite great variation in height), this character is often mistaken for Major Toht (Ronald Lacey), the film's primary antagonist, but it has been confirmed that they are not the same.