What is a wrathful Buddha? In reading this answer to another question there were many references to "the peaceful and wrathful buddhas" in the quote from The Tibetan Book of the Dead. This is a tradition that I'm not very familiar with. Is it possible to explain what a wrathful Buddha is and how Buddhist teachings on considering anger as a poison might align with the idea of a wrathful Buddha? Thanks for any clarification on this.
Wrathful Buddhas (or wrathful gurus for that matter) are not actually angry, in the way untrained people are. In Vajrayana before we even reach highest tantra, we learn to transmute emotions. If you are not good at it yet, at the very least you should be able to transmute anger into headache. Once you reach some mastery though, you can transmute any emotion into pure energy. When you have direct insight into the nature of mind, emptiness, attachments, and emotions - you can ride a wave of energy and even display wrath (an appearance of anger) without really taking it seriously. This is then used as a tool in those cases that demand such approach. Like getting angry at kids, you are half faking it, half letting yourself get carried by anger - to add your show more weight.