The tenth and eleventh Twelver imams, Ali al-Hadi and his son Hasan, were brought to Samarra and kept under supervision near the military cantonment, which is where the name al-Askari comes from. Both died there and are buried in the same shrine, along with the mother of the eleventh imam and the woman regarded as the twelfth's mother.
The doctrine that grew from the events of 874 is what makes the site central. Twelver Shia hold that Hasan al-Askari left a young son, that the son entered concealment to preserve his life, and that for some seventy years he communicated with the community through four successive deputies. When the last deputy died in 941 without naming a successor, the greater occultation began, and the imam remains alive and hidden until he returns as the mahdi to fill the earth with justice. A cellar within the shrine complex is associated with the concealment and is visited accordingly, though the belief itself does not depend on any particular room.
That doctrine shapes Twelver religious authority in the present, because in the imam's absence the qualified jurists exercise functions that would otherwise be his, which is the ground on which modern arguments about clerical government are conducted.
The shrine's golden dome was destroyed by a bomb in February 2006 and its minarets in 2007. The attacks were widely understood as designed to provoke, and they did: the months that followed were the worst of Iraq's sectarian killing. The dome has since been rebuilt.