Rishi Atri was the 7th Prajapati and and a son of Brahma, said to be ancestor of some Brahmin, Prajapatis, kshatriya and Vaishya communities who adopt Atri as their gotra. Atri is the Saptarishis (Seven Great Sages Rishi) in the seventh, i.e. the present Manvantara
He is among the Sapta Rishi (seven luminous or eternal sages in the sky) symbolized by the great bear and the seven stars around it. Named Megrez in Latin. The star is also considered as d (Delta) or the 4th star in the Great Bear constellation.
His wife name is Anusuya. Anusuya is the sister of Rishi Kapildev.
Attri Maharishi is considered to be one of the great discoverers of sacred Mantras of Hinduism. In his family line there were a few other seers of mantras namely: Shaavaashva, Avishtir, and Purvaatithi. There were also other great Rishis in that line: Mudgala, Uddaalaki, Shaakalaayani, Chaandogya, etc.
Attri-samhita and Attri-smriti are two works attributed to Attri.
Till the present day, a number of Brahmin families have this sage's name at the head of their lineage, which indicates that he or his descendents tutored that whole lineage.
Story of the birth of Datta, Soma and Durvasa
When Rishi Atri got the order from Brahmaji, to populate the world, he went to Rish Mountain to do penance with his wife Anusuya. After their hard penance, All three gods appear before them and ask for boon.
Rishi ne kaha mene tapasya putra ko prapt kerne ke liye ki hai, or aapke darsha chahe the, aap tino hi aagaye.Aap logo ki koi to kalpana bhi nahi ker sakta. Mujh per aisi krupa kaise hui? Aap hi batayae.
To which all three smiles and said:
Brahman! Tumhara sankalp satya hai. Tum jiska dyaan kerte ho hum tino wo hi hai- Ek ke hi tino Swaroop hai. Hum tino ke ansh se tumhare 3 putra(son) honge. Tum to krutarth roop ho hi.
After saying this they all went.Thus, Datta, Durvasa and Soma who are the incarnations of the Divine Trinity Brahma, Vishnu and Rudra respectively.
It is also said that - The trimurti channeled through Brahmarsi Atri when they granted boons to his wife Devi Anusuya for helping the Sun to rise in the east everyday. 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.
When the all three combine they called Dattatreya.

Avtars of Dattatreya.
Dattatreya incarnation of the Divine Trinity Brahma, Vishnu and Siva and his avatars- Shripad Shri Vallabha, Sri Nrusimha Saraswatiand Swami Samarth Maharaj.
According to the book "Shridattareya Shodashavatar Charitanee" by Shri Vasudevananda Saraswati, Dattatreya is supposed to have taken 16 Avatars. The names and their birthdate (as per the Lunar calendar) are given in brackets.[11]
1. Yogiraaj (Kaartik Shu.15)
2. Atrivarad (Kaartik Kru.1)
3. Dattatreya (Kaartik Kru.2)
4. Kaalaagnishaman (Maargashirsha Shu.14)
5. Yogijanvallabh (Maargashirsha Shu.15)
6. Lilaavishambhar (Paush Shu.15)
7. Siddharaaj (Maagh Shu.15)
8. Dnyaasaagar (Faalgun Shu.10)
9. Vishambhar (Chaitra Shu.15)
10. Maayaamukta (Vaishaakh Shu.15)
11. Maayaamukta (Jyeshtha Shu.13)
12. Aadiguru (Aashaadh Shu.15)
13. Shivarup (Shraavan Shu.8)
14. Devdev (Bhaadrapad Shu.14)
15. Digambar (Aashwin Shu.15)
16. Krishnashyaamkamalnayan (Kaartik Shu.12)
In the Dasopanta tradition, all 16 are worshiped and Dasopanta is considered as the 17th avatara.
In the Datta Sampradaya the first avatar is Shripad Shri Vallabh and the second is Narasimha Saraswati. Akkalkot Swami Samarth, Shri Vasudevanand Saraswati (Tembe Swami, Sawantwadi)) Manik Prabhu,Krishna Saraswati, Shirdi Sai Baba (Shirdi, Maharashtra), Gajanan Maharaj (Shegaon) and Pujya Sri Ganapathi Sachchidananda Swamiji are also considered as avatars of Dattatreya.[12]
The Upanishads Avadhutopanishad and Jaabaaldarshanopanishad mention that this philosophy was put forward by Dattatreya.
Durvasa (literally, one who is difficult to live with). Because he was born of Shiva's anger, he had an irascible nature. He is known for his short temper. Hence, wherever he went, he was received with great reverence from humans and Devas alike.
One more I want to say, when that daksh yagya happened, Datta and Durvasa both were went to penence. If durvasa rishi was there that time, nobody could save daksh from Durvasa's anger.