According to Sanatan Dharma, Manu was the first man in the world. Manu was born about 19700 years ago from today, and the name of the first Manu was Swayambhuva Manu, with whom the first woman was Shatarupa. He was called Swayambhu because 'Swayambhu' means self-born; born without parents). All the people of this world were born from the children of this first man and the first woman. Being the children of Manu, they were called Manav or Manushya. Swayambhuva Manu is also called Adi. Adi means beginning.
One day of Brahma is called a Kalpa. There are 14 Manus in one Kalpa. The period of one Manu is called Manvantara. At present there is Vaivasvata Manu (7th Manu). In Hinduism, there were 14 Manus (including Swayambhuva). 8 Manus were mentioned in Mahabharata & 14 Manus were mentioned in Shvetvarah Kalpa. There are descriptions of 14 Kulkars in Jain texts.
Manu is also the main character of the poet Jaishankar Prasad's Kamayani. The relation of Vaivasvata Manu mentioned in the Mahabharata can be linked to the hero of Kamayani.
Maharaj Manu ruled for a long time on this Sapta Dvipa Vati earth. People were happy in his kingdom. He composed the book Manusmriti, which is not available in its original form today. Its meaning has always been meaningless. In those days, the person who accepted or adopted the work was called Varna and Jati.