When Lord Brahma decided to create our universe, he created Seven Sages of India out of his thoughts they were called as Saptha Rishi or Manasa Putra (created out of mental thoughts).
They completely dedicated themselves to the pursuit of inner bless & divine light. They are known as "seers" as they are said to possess perfect knowledge about the past, present & future of humanity.
Atri is the rishi (sage) who composed the fifth Mandala (chapter) of Rig Veda. He proclaimed the theory of three strands of the sacred thread or Janeu/Janou. The three strands symbolize creation (represents Brahma and the letter "A"), sustainability (represents Vishnu and the letter "U") and destruction (represents Shiva and the letter "M"). Together these three strands show the vow that a Brahmin takes to recite and adhere to primordial sound AUM/OM.
Bhrigu or Bhrugu deliberately stepped on Brahma, Shiva and Vishnu to test the greatness of each God. Brahma and Shiva were furious but Vishnu treated the Sage with respect and declared the greatest. His descendants are supposed to have composed the Atharva Veda.
Angira alongwith Sage Atharvan is said to have composed Atharva Veda. He is also mentioned in the other Vedas.
He is credited to have created mantras. Godavari River was formed after he prayed to Lord Shiva. Shiva descended to Tryambakeshvar and this gave rise to the river Godavari. He is said to be the creator of Dharma Sutras that contain the rules for the four Ashramas, the forty Samskaras, the four Varnas, kingly duties, the punishments for various offences, etc.
He is the father of Gods and Demons. Sage Kashyapa is said to have two wives: Aditi (mother of Gods) and Diti (mother of demons).
He was chief of Saptarishis and the Rajaguru of the Suryavamsha (Solar Dynasty). Vasishtha is said to be the chief author of seventh Mandala (Chapter) of the Rigveda. He also wrote the "Vasishtha Samhita" - a book on Muhurtha/Muhurt that forms the basis of electional astrology.
He is said to one of the greatest of all Sapta Rishis. He is credited with spreading the vedic religion to South India and creating the Tamil language. He married Lopamudra, the human daughter of Brahma.