The speed running world record for completing the original Halo on its hardest difficult, Legendary, has just been set by 26-year old Canadian Andrew "goatrope" Halabourda who wrapped up the game in a tidy 1:38:57.
According the the SpeedDemosArchive, there are quicker runs - down to 1:20:51 - but these are captured in segments. 122 segments to be precise, captured between two runners, whereas Halabourda's run was all in one go, livestreamed last Friday (thanks, Kotaku).
For more info about what Halabourda is actually doing here, the Halo savant detailed some of his observations and tips in an "exhaustive trick list" and "when-do-fights-matter-list". Often the path of least resistance is the correct one, it would appear.
The previous world record for a single-segment Legendary run was also set by Halabourda at 1:41:15. Thus he bested his record by two minutes and 18 seconds. According to HaloRuns.com, the quickest anyone has completed the game in a single-segment run is 1:19:55 by LePhoque, but this was on Easy.
Watch how Halaboura's masterful Legendary speed run came together in his YouTube video below.