Bonacursus was a Cathar who converted to Catholicism and released a confessional report to the people of Milan exposing the nature of the Cathar heresy entitled Manefestatio haeresis catharorom quam fesit Bonacursus sometime between 1176 and 1190. He also reported on the Pasagian heresy as well as the Arnoldists.
References
Bonacursus Wikipedia(Text) CC BY-SA