Welcome to Humor Nation. Due to her inherited psychokinetic abilities, she was kidnapped and kept in the Hawkins National Laboratory where she was treated as a lab rat. Eleven escaped the captivity and ultimately met the gang of Mike, Dustin, and Lucas, and became good friends with them. She helped the boys in locating their lost friend Will. It was revealed that it was she who made a contact with a creature from the upside down and accidentally opened up a portal. Season 1 finale saw her destroying the monster to protect her friends, but she vanished in doing so. It was later revealed that she was indeed alive and has been living with Jim Hopper.
After being away from her friends for so long, she grew impatient and went on a journey to discover her past, and reunite with her friends. She again helps in defeating another Upside Down monster. At the end of seson 2, we see Jim Hopper adopting her as a daughter. Eleven has been deprived of friendship and socialization due to her captivity. That’s why in the beginning she was socially withdrawn and extremely careful of other humans. But she is very loyal and protective of her loved ones especially to Mike whom she shares a special bond with. She was even ready to sacrifice herself in destroying the monster when it became a threat to her friends.