Selyoid

The Selyoids were beings of pure light.

Biology
Seyloids were originally beings of light, but climate change caused their scientists to devise a corporeal form. Their corporeal from existed as a form of primordial soup capable of travelling through space on an asteroid. (PDA: Dying in the Sun)

Culture
On their own planet, the Seyloids lived purely to express their creativity, being a race of artists. Their scientists were considered to be outcasts. (PDA: Dying in the Sun)

History
The Seyloids once invaded Los Angeles and somehow changed various movies, including The Time Machine. The Second Doctor, Ben and Polly succeeded in stopping them. (PDA: Dying in the Sun, Synthespians™)

Behind the scenes

 * The name of the Selyoid obviously derives from celluloid, a chemical made in the production of film stock.