Mert was born in a tent, somewhere in Bulgaria, in the spring of 530 AD, to Macar Alp, and a concubine of his, from the Hephthalite Empire. His mother was named Bahar and she was his fathers favorite concubine. However, Bahar died soon after giving birth to Mert. When Mert was three, he, his father, and most of the tribe, moved into an area in Northern Hungary and Mert would spend much of his later life in Northern Hungary.
When Mert was five years old, he learned to ride a pony, a black pony, which he named Nur, meaning "light". Growing up, Mert was close to his horse, and went on many hunts with it, also learning horseback archery. Mert also learned wrestling as he grew up, and he grew up to be a strong, young man, often completing and winning in wrestling tournies in his village. Mert drunk lots of milk and ate whatever wild beasts he could find.
Growing up, Mert also became literate, learning to read and write in Latin and Greek, in case he would need to (for diplomatic reasons or trading) and he also learned to write Sanskrit. He became skilled at chess and was also interested in birds, studying whatever birds he could find.
After Macar died in a hunting accident, the 20 year old Mert succeeded him as khagan.