Hamas?

Remember that the Palestinian presidential palace was bombarded and destroyed by the Israelis who wanted him out of Palestine and dead as collateral. Arafat refused to leave palace so they destroyed everything except his office. At the end, the only way to get him out of there was if he was sick and rushed to hospital and that was what happen.

You could also claim that the Americans poisoned him to put their chosen president for Palestine, businessman Abu Massen.

You could also claim that his wife paid someone to bump him off. She was 42 and he was 75 and they were living apart for years. She inherited a couple billions of US aid money that Arafat siphoned off from the Palestinian people, to finance her luxurious lifestyle in Paris. She also demanded that there be no autopsy when he died. Maybe she had something to hide.