Hi, the other day i was reading the empire's book of warhammer, in which the first leader and hero, Sigmar, has some similar things with Connacht.
Also checking wikipedia i can confirm them (http://en.wikipedia.org/wiki/Sigmar):
"The night of his birth was marked with the appearance of a twin-tailed comet, which the human tribes took as a sign of great portent from the gods."
"Sigmar then went on a campaign to unite the disparate tribes of the future Empire, and one by one they submitted..."
"In his fiftieth year of reigning, Sigmar abdicated and set off to see what lay beyond the World's Edge Mountains to the east, in a similar fashion to the Dwarf ancestor/warrior deity Grimnir the Fearless, who legendarily strode off into the Chaos Wastes to do battle with the Powers of the Warp."
I doubt bungie copied them but there might be a link, a previous source both used. i know there are other aspects of myth similar to other "things", i dont mean myth copied them, just this called my attention when i was reading about Sigmar, the comet and his last travel to the east, where he never returned from for example, at least two coincidences in a same person/hero, and maybe more coincidences i dont see them right now.
About the previous source, the comet might be explained even with the christ's star, the one that guided the tree magic kings, the star moved so it was a comet, and this might be even be linked with other past beliefs, like the egipcian god Horus, with many similarities between both (Jesus and Horus).
About the last travel to the east i have yet to find something.