Hofund

Hofund is an Asgardian sword used by Heimdall. It also serves as a key to opening the Bifrost Bridge.

History
Heimdall uses Hofund as a key to open the Bifrost Bridge and transport people across the Nine Realms.

While warning Thor, Sif, Loki, and the Warriors Three about his oath to protect Asgard from invasion as they traveled to Jotunheim, Heimdall placed Hofund in a slot that activated the Bifrost Bridge. Heimdall used his sword in an attempt to attack Loki, but Loki simply froze him in ice with the Casket of Ancient Winters before the blow could strike.

Eventually, he was able to free himself, and he quickly cut down the two Frost Giants who had been left to guard the Bifrost, opening the Bridge for Thor and his friends using Hofund as a key.

During the Sacking of Asgard, Heimdall used Hofund to activate the shield around Asgard.

Heimdall drew Hofund to get Odin's and the Einherjar's attention to distract them while Thor, Loki, and Jane Foster were escaping in an Asgardian Skiff.

Trivia

 * In the comics, Hofund was made by the Dwarf smiths of Nidavellir, like Thor's hammer Mjolnir and Odin"s Spear Gungnir.
 * Hofund is most commonly used to open the Bifrost, but Gungnir was also used for this purpose by Odin and Loki.