In Norse mythology, Heimdall guards the rainbow bridge before Ragnarök.
Heimdall is the watchman of the gods and is associated with Bifröst, the bridge connecting Asgard with the human world. His extraordinary senses allow him to hear and see across great distances. The sources say he can hear grass growing and detect approaching dangers, emphasizing his role as a cosmic sentry.
Heimdall carries the Gjallarhorn, whose blast announces the beginning of Ragnarök. During that final conflict, he fights Loki, and the two kill each other. His duty therefore links the everyday security of the gods’ realm with the warning that begins the last battle.
Heimdall is not the guardian of the bridge toward Hel’s realm. That separate underworld route is associated with different figures in the surviving traditions. He is also not the same as Odin, even though both gods are connected with watchfulness, wisdom, and foreknowledge.