Ananta is a term meaning "endless" in Sanskrit. Shesha stems from the Sanskrit root meaning "that which remains". Adishesha means "the first shesha". When Adishesha coils forwards, time moves forwards and creation occurs, but when he coils backwards, the universe will cease to exist.
As Vishnu's companion, Ananta is sometimes reincarnated as a companion of Vishnu's avatar. When Vishnu was reincarnated as Krishna, Ananta took on the form of Balarama, Krishna's brother. When Vishnu had taken the form of Rama, Ananta became Lakshmana, Rama's brother.
Ananta is almost always depicted as a naga, a serpentine deity. He is sometimes depicted with 5 to 7 heads, but more usually with several thousand heads. Each head can also be depicted with an ornate crown. He is usually depicted underwater, sheltering Vishnu with his heads, who is reclining on him. Lakshmi is sometimes positioned at Vishnu's feet.