Sil was a human-alien hybrid created by the Search for Extraterrestrial Intelligence program.
Known as test subject S1L ("Sil"), she was conceived through the fertilization of a human egg with alien DNA. Sil was raised and monitored in a controlled laboratory environment until the scientists studying her attempted to terminate her life. Escaping her confines, she made her way to Los Angeles, where she evolved and succumbed to her alien instinct to find a suitable mate and partner; this led her to become a cunning yet hyper-sexual predator. She is the main character and antagonist of the 1995 film "Species".