Atri maharishi & Lord Brahma
Atri maharishi's one of the seven sons (Bhrigu, Vasistha, Bharadvaja, Jamadagni, Gautama, Visvamitra, and Agastya) of creator Lord Brahma. He is the ancestor of some Brahmin and Vaishya communities, who adopt Atri as their gothra. His name Atri means the possessor of Sat (pure), Raja (medium) and Tama (dark) qualities.
Mata or mother Anusuya is a daughter of kardama prajapati. She had three sons and one daughter including Soma, Dattatreya, and Durvasa and Shubhatreyi, who are the incarnations of define trinity Brahma, Vishnu and Siva respectively. The trinity channeled through Brahmarishi Atri when they granted boons to his wife devi Anusuya for helping, the sun to raise in the east every day.
Atri maharishi did great tapas on the Para Brahma, the fire / heat of the tapas became unbearable to the whole world, and Lord Brahma had to accept it and gave it a form of a man. He also granted a boon to sage Atri. The boon was that at the right time a son would be born to him. As he continued the tapas, the Trinity of Brahma, Vishnu and Siva (Rudra) appeared before the sage. To his question, they replied that they were all equal with different roles and pleased with his great penance they promised to be born as his children. Soma is called Chandratreya or Chandratre, and Durvasa is Krishnatreya or Krishnatre.
Somatreya (Chandra) established the Someshwara Jyotirlinga, used to overcome all kinds of passion. Soma as the incarnation of Brahma, has the power to cause any species to continue survival. Soma (Chandra) and Durvasa gave their powers to Datta (Amsa of Vishnu) and went for Tapas etc. Datta, or Dattatreya as he prefers to be known thus carries all the powers and attributes of the Trinity and thus the Nirguna Para Brahma Tatwa and became a Guru and continues even now.
Sage Atri is the first among the Sapta Rishis (seven luminous or eternal sages in the sky) symbolized by the great bear (Ursa Major) and the seven stars around it.