In "Stranger Things," the test-subject number identifying Kali Prasad is Eight. She is also called 008, the designation she received during her time as a child test subject at Hawkins National Laboratory.
Kali appears in the second-season episode “Chapter Seven: The Lost Sister.” Like Eleven, she was taken by Dr. Martin Brenner and subjected to experiments. Her ability differs from Eleven’s: Kali can create vivid mental illusions that alter what other people perceive. The series presents this shared history as the reason Eleven regards her as a sister, not because they are established as biological siblings.
Kali escaped the laboratory and later lived in Chicago with a group of runaways. Her experiences made her more focused on revenge against people connected to the lab. When Eleven finds her, Kali encourages her to draw on anger to strengthen her abilities, but Eleven ultimately leaves to protect her friends in Hawkins.
The number is easy to mix up with Eleven’s 011 designation. “Eight” identifies Kali, while “Eleven” identifies Jane Ives; both names come from the laboratory’s numbering system.