Formed in S?upsk in mid-1989, Betrayer featured Wojciech Moli?ski (vocals/drums), Maciej Maciejewski (guitar) and Mariusz Zieli?ski (guitar), with bassist Maciej Ró?a?ski later added.
March 1990 saw them record the Forbidden Personality demo, featuring 7 thrash metal tracks. In May of that year, Rozanski left, replaced by ex-Slaughter bassist Piotr Kuzio?a, with Berial taking the vocal duties. The Necronomical Exmortis demo then followed featuring a more death metal sound.
By early 1991, the band had signed with 'Carnage Records', but that September, Zieli?ski committed suicide. Former Slaughter guitarist Maciej "Ripper" Krzysiek was soon later recruited to take his place.
Kuzio?a joined Vader for a short time but soon returned. Moli?ski left the group to join Mortify, taking drum duties at first then switching to bass.
The band would carry on with this line-up to release Calamity (1994). Infernum in Terra followed in 2015 after the 2012 reformation with the line-up of: Berial (Vocals/Bass; ex-Vader, ex-Slaughter), Krzysztof Tubaja (Guitars) and Arkadiusz Kozakiewicz (Drums).