"Corbeau" is a guardian who brings good news. In alchemy, the "Corbeau" is the symbol of the first stage L'oeuvre au noir". He appears several times in the Liber Motus (Le Livre Muet). Book which consists only of drawings, no text, and explains all the stages of alchemy, but in the wrong order.
in the wrong order... in order to preserve the secret. Every time the "Corbeau" shows up, he comes to tell the the alchemist that he is on the right track and that he will soon evolve to the next stage.
This is in contrast to other cultures where the "Corbeau" announces bad news and death.