I currently have a mentor that's been instrumental in my development. I feel incredibly lucky to have them in my professional life, and think it's invaluable. I wouldn't be where I am without their help.
I met them at work on a project (I was in a different part of the company at the time). They were the more senior person running the project, and saw my interest and started helping me toward my goals. It was a pretty organic process.
I wish there was a more organized process to get a mentor, especially in areas outside of your current job. It's difficult to meet people in general, and the kind of person that is open to mentor is a small, special group.
I've never mentored anyone but given my experience I look forward to doing it one day very much.