Seven Immortals(Chiranjivi) in Hinduism

Chiranjivis are the "immortals" in Hinduism who are to remain alive throughout this Kali Yuga until the start of next Satya Yuga.

In Hinduism, "immortal" does not mean eternal. Even "immortal" outer bodies are dissolved at the end of the universe, along with that of its secondary creator Brahma.
At the end of one universe, i.e. at the end of one Kalpa and the beginning of another, a demon attempted to become eternal by "swallowing" the Vedas as they escaped from Brahma's mouth, but the Vedas were restored by Vishnu's avatar, Matsya. Vishnu also killed other asuras like Hiranyakasipu and Ravana who tried to become immortal by obtaining boons from Shiva.

The Seven Immortal

In Hindu theology, it has been expounded in several puranas and epics like Mahabharata and Ramayana that there exist seven long lived personalities, in the Hindu pantheon. On the earth they have been considered exceptions. They existed in the past ages - Satya Yuga, Treta Yuga, Dvapara Yuga and are still there in Kali Yuga.

These Eight chiranjeevis are:

• Bali Chakravarthi, who was granted the boon by Vishnu that he can have his desire fulfilled of being the next Indra, before merging with Vishnu. He expounds the virtues of valour and charity.
• Parashurama, an avatar of Vishnu, he signifies one who is the master of all astras , sastras and divine weapons.
• Vibhishana, brother of Ravana in the Ramayana. Vibhishana surrendered to Rama before his battle with Ravana and was crowned king ofLanka after Ravana was killed by Rama. He was a faithful follower of Lord Rama and stands for righteousness.
• Hanuman, who served Rama, stands for selflessness, courage, devotion, energy, strength and righteous conduct
• Vyasa, a sage who narrated the Mahabharata, and was also a sage in the epic, he represents erudition and wisdom.
• Ashwatthama, the son of Drona, he was supposed to be a great warrior, but acted out of cowardice to punish his father's death and got cursed.
• Kripa, another military teacher of the princes in the Mahabharata.

A mantra, about the seven immortals, is said to give human beings good luck and long life if recited everyday:

"Ashwathaama Balir Vyaso Hanumanash cha Vibhishana Krupacharya cha Parashuramam Saptaita Chiranjeevanam"

which means Ashwathama , MahaBali ,Vyasa ,Hanuman ,Vibhishana ,Kripacharya,Markandeya and Parashurama are the 7 long lived personalities.according to another legend Markandeya also chiranjeevi.