Hela is the goddess of death and the ruler of Hel. She will appear as the main antagonist of Thor: Ragnarok.
This version of the mythological Hela was created by Stan Lee and Jack Kirby.
Marvel Animated Universe
The Avengers: Earth's Mightiest Heroes
Hela was the ruler of Niffleheim, the land of the dead. Captain America was transported into her realm and tried to convince him to stay. Hela was well aware of her father Loki's plans and played along with them, but knew her father very well, and was aware of eventual betrayal.
Hela negotiated with Captain America, and transported him to Asgard to aid his team, on the condition that should he fall in battle, his soul would belong to her.
At the Mansion, Cap saw a reflection of Hela on his broken shield just before he was ambushed by a Skrull imposter.
She was shown to be bored pairing her skeleton minions against each other until Loki arrives to cut a deal with her. In exchange that Hela lends Loki the Horn of Hela to control her skeleton minions, she can get entertained by watching Hulk and Thor fight each other. Loki ends up tricking Thor and Hulk into heading to Valhalla where Hela makes them fight each other. When Hulk even tried to attack Hela, she temporarily transformed him back into Bruce Banner and then transformed him back into Hulk. After letting Hela send them back to Earth to continue their fight there, Hulk and Thor fight Loki where they take a dive against him. Hela deems Loki the winner of the fight as she has the giant skeleton that Loki formed take Loki back to Valhalla to keep her entertained in his fight against her skeleton minions.