Jeffrey K. Marsh also known as Jeff "Swampy" Marsh and Swampy (born December 9, 1960) was a director and one of the writers of the Nickelodeon program Rocko's Modern Life. Co-creator of Phineas and Ferb with Dan Povenmire, he has directed, written, and acted in this hit Disney Channel and Disney XD original series. In Phineas and Ferb, he portrays the voice of Major Monogram, the commander of Perry the Platypus.
From the show's inception, Marsh has been one of the main songwriters for the series, along with Dan Povenmire as well as Martin Olson.
During the time in England, friends began calling him "Swampy" and "Boggy", playing off of his last name. He told them that he did not want to be called "Boggy". After his return to the United States, other friends heard of his nickname and also began calling him "Swampy". After a while, Jeff began to like it.
He is the grandson of world-renown band leader and songwriter Les Brown.
Currently married; wife of Dutch descent, which explains why Phineas and Ferb has so many references to the Netherlands, such as Buford Van Stomm's last name, Florraine from Imperfect Storm only speaking Dutch, and Paolo Vanderbeek being part-Dutch.