Sheila (Elementary, My Dear Sheila)

Sheila was a Sentient, one of the original species from the birth of the universe. She was made up of sentient helium atoms, enclosed in a balloon, and was a friend and companion of the masked Mexican wrestler, Señor 105, whom she met in Paris. (PROSE: Elementary, My Dear Sheila)

Behind the scenes
On Paul Hanley's account, he revealed that the balloon held by David Bowie on the back cover of Lady Stardust may contain Sheila.