Instigator of the First Crusade, Peter the Hermit
(Though it may be noted he did not attain the fanaticism of
encouraging his followers to deliberately kill themselves to murder
more of the non combatant 'enemy').

According to an eye witness of the capture of Jerusalem
1109,
Gesta Francorum,
The crusaders 'also ordered all the Saracen dead to be cast outside
because of the great stench, since the whole city was filled with their
corpses; and so the living Saracens
dragged the dead before the exits of the gates and arranged them in
heaps, as if they were houses. No one ever saw or heard of such
slaughter of pagan people, for funeral pyres were formed from them like
pyramids, and no one knows their number except God alone.'
And some rather belated Muslim copycats, who have attained new heights
of depravity:
Both Sunni
Dr. Abdel Aziz al-Rantissi
and
Sheikh Ahmed Yasin (of Hamas)