Anderson was conceived backstage during Pink Floyd's 1977 In the Flesh Tour for their album Animals (which included songs from Wish You Were Here). The progressive rock band used what became an iconic giaint inflatable pig during the concert. The dogs and sheep used in the concert needed water, and the pig needed water and a pigstie for a roll in the mud. So roadies had filled a plastic swimming pool with water to be used by the animals during breaks in the concert.
What the band and crew didn't know was that an interdimensional female dolphin humanoid alien from Sirius (the dog star) had moved into the backstage pool to keep wet and to avoid paying for a ticket.
While the band was performing, Waters become upset with a fan and spit in his face. The fan, John Anderson, looked for a place to wash off and found the pool. Pink Floyd was then performing songs from its Wish You Were Here album. John saw the dolphin-human woman and she invited him in. He went in. While the band was performing "Have a Cigar," John impregnated her.
Twelve months later, Floyd was born in a bathtub. John handed out cigars.
When Floyd was born, he appeared to be entirely human. Except for a blow hole on top of his head. And having no hair. And having smooth hairless grey skin, flippers for hands and feet, and a tail. And a dolphin nose and teeth. Other than that he looked entirely human.