Diablo 3: the world’s first Hardcore Inferno completion

A significant step-up from hell difficulty, the Inferno difficulty is the hardest in the game. The completion was actually done before the release of patch 1.0.3, which makes the game "easier" to play and complete the difficulties prior to Inferno. The most impressive thing about this achievement was that it was done using a hardcore character. Hardcore characters are lost forever when they are killed, there is no going back.

On Tuesday 19^th June, player Kipparrian from Toronto Canada completed all four difficulties with a hardcore Barbarian (with help from a Wizard named Kippi). After initially casting doubt on the achievement status as a world first, Blizzard community manager Bashiok pit his official stamp on it, saying:

 "My apologies Kripp and Krippi, looks like you were 1st HC Inferno clear," he tweeted. "(my spreadsheet deciphering isn't what it used to be) Congrats!"

Below is the video showing the lengthy, tense Diablo kill, with explanation from Kripparrian.
Warning: There may be spoilers.