Gautam Rishi is among the Saptarhṣi or Seven great sages. He was one of the Maharishis of Vedic times who discovered Mantras in Sanskrit. The Rig Veda has several 'hymns' that go with his name. He was the son of Rahugana. He married Ahalya and had two sons Vamadeva and Nodhas both themselves discoverers of Mantras. Ramayan (Treta Yuga) and Mahabharatha (Dwapara Yuga) have references to Sage Gautam as he lived during these two Yugas.
Sage Gautam's sixty-year-long penance is mentioned in the Shanti Parva of the Mahabharata. He is the progenitor of the Gautama gotra. Lord Indra in disguise of Gautama Rishi with Ahalya.
As per Brahmanda Purana, one of the sub-branches of the Raanaayani branch of Sama Veda was initiated by Gautam. Some famous disciples of Gautam were Shaandilya, Gārgya, and Bharadvaja.
When the battle of Kurukshetra was going on, Dronacharya took over the commandership of the Kaurava army and got ready to destroy the entire Pandava army. At that point, Gautama entered the battlefield, addressed the Drona, "stop the killings and give up arms. You are fighting a battle against your Varn-ashram dharma. Embrace death and go to heaven". Drona, giving respect to the words of these sages, gave up his arms and left the battlefield. As advised by sage Gautama, he went to heaven by the Yogadharana way.
Sage Gautam used to travel all over the world to help people. Sage Gautam had mastered the great Savitri Mantra. Sage Gautama was the one to whom the great Vyahrthimanthra 'Janah' was revealed. He was a great Tapasvi. He was devoted to God and a generous host. The Narada Purana describes the story of the 12-year famine during which sage Gautam fed other sages and saved them. Once the country was reeling under a great famine, but owing to the virtue of Sage Gautam, his ashram dwellers had not experienced the calamity. Thousands of sages took refuge in his ashram. Sage Gautam welcomed everyone with open arms and played host to them. The famine continued for years, but Gautam offered them great hospitality.