Habash was the founder of the Popular Front for the Liberation of Palestine (PFLP), a Marxist-Leninist movement calling for the total abolition of the "zionist entity" by military means, with no negotiation or compromise. This included fighting to overthrow the Jordanian government of King Hussein so that Jordan could be a base for revolutionary war against Israel.
The PFLP engaged in a protracted list of terrorist incidents, one of the highest profile being the hijacking of four airliners in 1970 in the so called "Dawson's Field Hijackings". It rejected overtures of peace from the PLO, and has opposed any settlement with Israel.
good riddance to Habash, he was no friend of peace.