As per Vedas Brahma was born from the energy of Vishnu. From Brahma were born the four great saints, who are Sanak, Sanandan, Sanat and Sanatan. In our Universe, these four 4 saints are the eldest children of Brahma.Due to asexual birth from the mind of their father alone, they have no mother. Being liberated souls and experts in Science of Yog, they were empowered to help others attain liberation through spiritual sadhana. After the 4 saints, came the 7 sages namely Mareech, Angira, Atri, Pulastya, Pulaha, Kratu and Vasishtha. They were empowered with the task of procreation of the human population.Then come the 14 Manus namely Svayambhuva, Swarochisha, Uttam, Tamas, Raivat, Chakshusha, Vaivasvat, Savarni, Dakshasavarni, Brahmasavarni, Dharmasavarni, Rudra-putra, Rochya and Bhautyaka. They were empowered for the administration of humankind and for the establishment and protection of Vedic Dharma.
We are currently in the era of the 7th Manu , who is called Vaivasvat Manu.This era is also called Vaivasvat Manvantar.
In the present kalp(day of Brahma), there will be further seven more Manus.
In a nut shell we can say that Lord Vishnu is the the original forefather of all forefathers.