Lord Ananta Śeṣa 

His name means "that which remains", when the world is destroyed at the end of a Kalpa ( A relatively long period of time (by human calculation)), Śeṣa remains as he is.

The magnificent incarnation of Lord Maha Vishnu himself. He is the king of all Nagas.

Śeṣa is depicted as a massive coiled form  that floats in space or the Ocean of milk, to form the bed which Lord Vishnu lies upon accompanied by his consort Mother Lakshmi.

According to the Mahabharata Śeṣa was born to sage Kasyapa and his wife Kadru. Kadru gave birth to thousands of snakes of which Śeṣa was the eldest. A lot of Śeṣa's brothers were cruel in nature and were bent of inflicting harm on others. Disgusted by this behavior he left his mother, and to ascetic penances (deep meditation), he lived on air, and meditated in many places including Pushkara and Himalayas. By seeing his will lord Brahma asked Śeṣa to request a boon, in which he asked Brahma to be able to control his mind so he may continue in his deep meditation, in return Brahma asked of Śeṣa to go beneath the unstable earth and stabilize it.    

Lord Ananta is the predominating Deity of the material mode of ignorance as well as the false ego of all conditioned souls. When living being thinks, "I am the enjoyer, and this world is meant to be enjoyed by me," this conception of life is dictated to him by Sankarsana. Thus the mundane conditioned soul thinks himself the Supreme Lord. This great universe, situated on one of Lord Anantadeva's thousands of hoods, appears just like a white mustard seed. It is infinitesimal compared to the hood of Lord Ananta. At the time of devastation, when Lord Anantadeva desires to destroy the entire creation, He becomes slightly angry. Then from between His two eyebrows appears three-eyed Rudra, carrying a trident. (SB 5.25.1 - 3)

A. C. Bhaktivedanta Svāmi Śrīla Prabhupāda said " sankarsana of the quadruple form descends with lord Sri Rama as Laksmana. when Lord Sri Rama disappears. Śeṣa again separates himself from the personality of Laksmana. Śeṣa returns to his adobe in the Patala region, and Laksmana returns to his abode in Vaikuṇṭha.

in the Bhagavad-gita, chapter 10, verse 29, Sri Krishna while describing 75 of his common manifestations, declares ,"anantaś ca asmi nāgānāṁ" : of the nagas, i am Ananta.

Patala denotes the seven lower regions of the universe which are located under the earth, often translated as the underworld or netherworld. (NB.this will be discussed in detail later on in the blog)

NB. Vaikuṇṭha will be discussed later on in the blog.