Abdullah ibn al-Mutazz

Abdullah ibn al-Mutazz In the case for Arab-Islamic history, Abdullah ibn
Al-Mutazz may have the shortest reign, although many historians don’t
consider him a caliph. In 908, a 13 year-old kid was chosen to rule by the
military and the kid’s mother over his elder cousins. One of them was an
ingenious poet and former member of the state councils called Abdullah
ibn Al-Mutazz. However the bureaucracy headed by the vezier and the
heads of diwans were against him and in 909 conspired to put their former
colleague Abdullah as Caliph and on one July day the coup happened and
he was proclaimed caliph. When he went to sleep the military made a
counter coup (the troops were outside Baghdad then) and killed the Caliph
the same day he was formally coronated. He is still called the one day
caliph.