(written from a Production point of view)
Born in Boston, Massachusetts, Themmen first entered the stage at the age of six and performed in plays such as Iphagenia in Aulis (1966), Mame (1967), and The Rothschilds (1973). In 1971 he portrayed Mike Teevee in Mel Stuart's fantasy musical Willy Wonka & the Chocolate Factory. Themmen also worked on several television commercials before he attended the New York University and received his Bachelor of Fine Arts in Theater.
As a former child actor, Themmen lent his voice to the animated short film Macross Plus (1994, along Skip Stellrecht and Dan Woren), had background parts in movies such as The Doors and The Big Lebowski, and was interviewed for several specials about Willy Wonka & the Chocolate Factory (2001; 2003).
Themmen later became a business manager for Disney's theme parks and has worked as a casting director for commercials in Los Angeles.