What's the Name of That Book??? discussion

This was a book series. The demon Az was summoned by his wizard friend in order to impress the wizard's apprentice. However, the wizard dies leaving Az in the human realm. The apprentice is not advanced enough to send Az back. The books follow Az and the apprentice on their journey and learning magic.

Thanks for any help!

This is the Myth series by Robert Asprin
Another Fine Myth

I loved this series.

Robert Asprin! Yes! Thank you soooo much!