They are 7 Chiranjivi (immortal living beings in Hinduism who are to remain alive on Earth through this Kali Yuga till its very end).
In Hinduism, immortal does not mean eternal, as all physical bodies are foretold to become immaterial at the end of time, along with Brahma himself, with the destruction of the Universe.

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

Below are the seven death-defying or imperishable personalities
Ashwathama
King Mahabali
Vyasa
Hanuman
Vibhishana
Kripacharya
Parashurama