Krathu

Kratu (the great Prajapati is the name of the great Rishi Kratu, which appears in two different ages. In the Swayanbhuva Manvantara, Kratu was a Prajapati and a very dear son of Lord Brahma. He was also the son-in-law of Prajapati Daksha. His wife was named Santhati. It is said that he had 60,000 children. They were named as included in the Valakhilyas. Kratu also had 2 sisters, Punya and Satyavati.

Before he was married, Kratu was a good friend of Lord Rudra (Lord Shiva). Rudra was originally called Pasupati, the Lord of Beasts. It appears, though, that he gave away his authority of Pasupati to Kratu when Kratu punished Rudra's father Brahma for his sinful activities.

Later, the demigods divided all the beasts among themselves without giving any share to Rudra and without considering Rudra, as he was initially considered a non-Aryan god. Rudra went to Prajapati and told him that he would kill all the demigods. Prajapati asked him to wait and promised him that soon he would restore the title to Rudra. The demigods then proceeded to perform a sacrifice without inviting Rudra. The head of the sacrifice was none other than Prajapati Daksha, who was nursing a grudge against Rudra or for the simple reason that his daughter Sati married Shiva against his wishes. He did not send even an invitation to Shiva, who was his son-in-law.

Sati went to the sacrifice uninvited anyway, and was terribly insulted for marrying a beggar. She was not able to listen to the insults hurled at her by her father and her sisters. She committed suicide by jumping into the sacrificial fire.

Hearing the news, Lord Shiva became mad with rage. He pulled out a lock of hair from his head and threw it down, invoking the Spirit of Veerabhadra or Bhairava. He ordered Veerebhadra to go with his followers and destroy everybody who attended the Yagna, including Prajapati Daksha. Accordingly, they went and be-headed Daksha. Then they started punishing each and every god who attended the holy sacrifice. They knocked out the teeth of Pushan, took out the eyes of Bhaga, and severed the two testicles of Kratu.

All the gods went to Shiva and begged for his mercy. Shiva said that they should all serve under Him as animals for some time; only then would they will regain their original status. All the gods agreed to this. Shiva then restored the teeth, eyes and testicles of the different Gods. Daksha was also revived by placing the head of a goat on his neck. After his testicles were restored, Kratu married Sannati (Santathi), the daughter of Daksha. They were all pygmy sages no bigger than the joint of the thumb. They were all chaste and pious. All were Brahmacharis and students of Vedas. (References: Maitreya Samhita 4-2-12 And Brahmanda Purana)

Rishi Kratu was again born in the Vaivaswata Manvantara because of Lord Shiva's boon. In this Manvantara he had no family. It is reported that he was born from the hand of Lord Brahma, whereas other Rishis are described as having been born from other parts of the body of Lord Brahma. (Reference –Bhagavat). As he had no family and no children, Kratu adopted Agastya’s son, Idhvaaha. Kratu is considered as one of the Bhargavas. In Matsya Purana it is said that his mother's name was Poulomi. He is also considered as one of the Viswa Devas.

References

1. http://www.godchecker.com - Indian mythology(Kratu the Indian God of Wisdom)
2. http://www.indianet zoned.com/34/kratu-indian sage.htm
3. http://www.indian scriptures.com/gurus/prajapati kratuI-I
4. https://books.googlde-co.in/books?id/rishi_kratu
5. http://www.harekrsna.com/sun/features/Kratu Rishi