Piotr Paweł Wiwczarek (born 22 October 1965 in Olsztyn, Poland), also known as Peter, (ex nickname Behemoth) is a Polish musician who is the vocalist and lead guitarist for the death metal band Vader, as the only constant member of the band since its inception.

[1] He has also collaborated with Kazimierz "Para" Paraszczuk on his tribute album, Bandid Rockin', and is the producer of several of Vader's releases.

He is also the founder and guitarist of a side-project, named Panzer X. Wiwczarek also became a producer for the first time in 1999, when producing the Polish death metal band Decapitated's first release, Winds of Creation.