In 1990, Henning Rümenapp, Dennis and Stefan Ude found the Guano Apes. The singer, Sandra Nasic, completed than band in 1994. In 1997, they recorded and released their first album "Proud like a god". The album stayed in the German charts for more than a year. The singles "Open Your Eyes" and "Lords of the Boards" (a work commissioned for the Snowboard World Championships) were huge hits and are still famous today.
Thanks to the album they went on a 18-month tour through Europe and the United States. That earned the band international success. The album sold about 3 million copies. After disbanding in 2006, they re-formed in 2009 to record the latest album Bel Air.
During the hiatus of Guano Apes, Dennis has been busy with two side projects, Tamoto and iO.