Agni - Epic Characters of Vedas & Upanishads

Agni is one of the ashtadikpalakas who protects the South-east direction (Agneya). He occupies the second position after Devendra and is the chief deity of the Rig Veda. The Maruth devas are born out of Agni. Agni is present in every living being or thing and is the energy that causes movement. He is Varuna's brother and is influenced by Vayu Deva. According to Vishnu Purana, he is the eldest son of Brahmadeva.
Agnideva was once cursed by sage Bhrigu because of which he entered the ocean and performed tapas. The world was on the brink of disaster without Agni. Brahmadeva had to implore Agni to go back to the world and resume his duties. Agnideva once lost his immense power of digestion when King Swethaki performed a great yajna lasting  a hundred years.   As suggested by Brahmadeva, he had to burn the Khandava forest in order to regain his power.
In spite of burning down a large part of Sahadeva's army, Agni  stopped his burning spree on  Sahadeva's plea and helped the Pandavas to complete the rajasuyayajna.  Devendra had once committed a sin of killing a Brahmin. When Brahma divided the sin into four parts, Agni accepted one of the parts in order to free Devendra. Agni appears in the Ramayana when he himself offered a pot of payasam to the childless Dasharatha.
Later, when Sita was put through a test of fidelity, he announced to the world that she  was  the most faithful woman of her time.  Parameswara blessed Agni saying that he would never have to fear death.  Agni Deva is all powerful, present in all, sustaining and protecting all the time.