Ki-Adi-Mando was the current Fandalore or in normal terms: the president of a Mandalorian fan club called The Fandalorian Crusaders. This position allowed him to wear a life-sized replica Jango Fett's helmet on his cone at their official meetings. He also had the "pleasure" to meet with Karen Traviss every two weeks to plan their next strategy on how to make the Mandalorians more popular. He drove an '83 Honda Civic hatchback which he called Slave VII.
It was on his orders that the Fandalorians built and named (with the aid of his super sized brain) Fandalore, the planet of the Fandalorians. But when Palpatine heard, he couldn't resist destroying it. Ki-Adi-Mando was not at home when it happened.
He died at the hands of Cassus Fett the Lesser, who beat Mando to almost to death with a 2x4 (with nails) and then decapitated him (strangely fulfilling Ki-Adi-Mando's dream of death by decapitation, the same way his hero went out). The Lesser Fett then stole Ki-Adi-Mando's Jango Fett helmet off the corpse and put it on his own head (which, it must be noted, did not have much in the way of brains). This made Cassus Fett the Lesser the new Fandalore of all Fandaloria.