Bhagavan Sri Ramana Maharshi was probably the most famous Indian sage of the twentieth century. He was renowned for his saintly life, for the fullness of his self-realization, and for the feelings of deep peace that visitors experienced in his presence. So many people came to see him at the holy hill of Arunchala where he spent his adult life that an ashram had to be built around him. He answered questions for hours every day, but never considered himself to be anyone's guru.
He was born on December 30, 1879 in a village called Tirucculi about 30 miles south of Madurai in southern India. His middle-class parents named him Venkataraman. His father died when he was twelve, and he went to live with his uncle in Madurai, where he attended American Mission High School.
At age 16, he became spontaneously self-realized. Six weeks later he ran away to the holy hill of Arunachala where he would remain for the rest of his life. For several years he stopped talking and spent many hours each day in samadhi. When he began speaking again, people came to ask him questions, and he soon acquired a reputation as a sage. In 1907, when he was 28, one of his early devotees named him Bhagavan Sri Ramana Maharshi, Divine Eminent Ramana the Great Seer, and the name stuck. Eventually he became world-famous and an ashram was built around him. He died of cancer in 1950 at the age of 70.
At age 16, he heard somebody mention "Arunachala." Although he didn't know what the word meant (it's the name of a holy hill associated with the god Shiva) he became greatly excited. At about the same time he came across a copy of Sekkilar's Periyapuranam, a book that describes the lives of Shaivite saints, and became fascinated by it. In the middle of 1896, at age 16, he was suddenly overcome by the feeling that he was about to die. He lay down on the floor, made his body stiff, and held his breath. "My body is dead now," he said to himself, "but I am still alive." In a flood of spiritual awareness he realized he was spirit, not his body.
Ramana Maharshi didn't have a human guru (other than himself). He often said that his guru was Arunachala, a holy mountain in South India.
Source : http://www.realization.org/page/topics/ramana.htm