Heimdall

Heimdall is the guardian of the Bifrost and a protector of Asgard. While Loki remains imprisoned, Heimdall performs his duties near Loki's magical prison, unaware that Loki has devised a way to manipulate him without directly attacking him.

Loki causes a leaf to strike Heimdall's eye, making him shed a tear. That seemingly insignificant event is actually the key to Loki's escape because the tear breaks the enchantment imprisoning him.

Heimdall guards the Rainbow Bridge connecting Asgard and Earth. His responsibility includes monitoring those who attempt to pass between the realms. Loki's escape and movements through Asgard occur while Heimdall continues to serve as the guardian of the bridge.