Yogi is a person who practise Yoga.
Yoga is not just a form of exercise it is uniting Body Mind and Soul.
According to Hindu ancient text Patanjali, there are eight limbs of yoga
A real / perfect / true Yogi is a God in flesh.
The one who is deprived of lust, greed, jealous, ego, anger, pleasure
The one who not differentiate between happiness and sorrow
The one who not differentiate love and hatred