What is a mentor? According to Greek legend, the goddess Athene liked to come down to earth disguised as a man named "Mentor" so she could advise the young son of Ulysses. (The Greek root "men" means remembering, thinking or counseling; we still use it in words like "mental.") Today, a mentor is an experienced and trusted counselor, anyone who guides and encourages another, especially someone younger.
Mentors come in all shapes and sizes, formal and informal. Usually your mentor is someone who takes a personal interest in your progress, seeing your potential and regarding you as just a bit more capable and talented than you think you are. Not too much more, or you'll dismiss their opinion as unrealistic. Not any less, or you'll have nothing to strive toward.
In my own life, I've had many excellent mentors – wise bosses who guided me and exciting clients who encouraged and inspired me to be the best I could be. We all have mentors who don't know they are our mentors. They are all around us as we watch and learn from what they do and say. Many people have told me I had been their mentor the first time we met.
Good mentors are the people who put the gas in your tank and give you a road map to where you want to go.