http://www.eldridgefinancial-blog.com/2012/02/eldridge-financial-blog-content-collection-mentoring-advice/

Everyone who’s gone through the early stages of an academic career has had an undergraduate research supervisor, and a Ph.D. and postdoc adviser. But not everyone can claim to have had a mentor. Even fewer can claim to have had more than one. And that’s too bad.

The essential difference between an adviser and a mentor is that the adviser directs while the mentor guides. An adviser often has an agenda, be it to point your research in a particular direction or merely to publish more papers. Foremost among a mentor’s concerns are your professional development and personal well-being. A mentor offers you support, guidance, and even solace with no other motive than helping you identify and reach your own goals. A mentor is someone you can open yourself up to without fearing deleterious consequences.

If you are lucky, your adviser is also a mentor, but many mentors are found outside of the lab.

It is also common — and recommendable — to have several mentors, each contributing a unique approach to your problem or situation to help you broaden your perspective. As you move up the career ladder, you should also expect your mentoring needs to change. A new mentor may be needed.