As one of the top negotiators in talks to bring the Gaza war to an end, Haniyeh was criticised by some on his own side over his approach to the conflict.
ADVERTISEMENTIsmail Haniyeh, the 62-year-old leader of Hamas's political wing and a prominent face of the organisation for decades, has been reported killed in an airstrike on his residence in Tehran.
It is as yet unclear whether or not the strike was carried out by Israel, but regardless, it strikes at the heart of one of the Middle East's most important Islamist organisations.
Observers say Haniyeh's death has dealt a significant blow to Hamas at a time when tensions are flaring in the Middle East over the devastating war in Gaza and raised questions about the future of negotiations between the militant group and Israel.
In recent years, Haniyeh ran the militia group's political office from exile in Qatar, but his career stretches back decades.
Born on 29 January 1963 in the al-Shati refugee camp in the Gaza Strip, Haniyeh began his political career by closely aligning himself with Hamas founder Sheikh Ahmed Yassin, joining the paramilitary group during the First Intifada in the late 1980s.
Imprisoned several times for participating in the intifada in Israel and later leaving Gaza, he rose to become an important Hamas leader.
Nicknamed "Abu al-Abd", he was appointed as a member of the secretive "collective leadership" team in 2004 after Sheik Ahmed Yassin and Abdel Aziz Rantisi — Hamas' two previous leaders — were killed by Israel.
He first became the prime minister of the Palestinian Authority in 2006, following Hamas' victory in the Palestinian parliamentary elections, and has gained international attention ever since.
In 2017, he succeeded Khalid Mashael as head of the Hamas Political Bureau and was declared a wanted terrorist by the US soon after.
Then-US President Donald Trump's administration had said the move was aimed at cutting off Haniyeh's access to international financial resources.
In the wake of the 7 October attack on Israeli territory, in which Hamas fighters killed at least 1,200 people and took more than 200 hostage, Haniyeh became a key figure in negotiations to end the ensuing war in the Gaza Strip, which local Hamas-run health authorities claim has killed more than 39,000 Palestinians.
Israeli officials have several times held him responsible for the failure of peace talks and blamed him for refusing to release the hostages still alive in captivity in Gaza.
Despite holding a leadership position, Haniyeh faced his share of criticism from within Hamas on more than one occasion since the start of the war.
There were reports of disagreements between him and Yahya Sinwar, the military leader of Hamas inside Gaza, over both the approach to the ceasefire negotiations and military strategy.
Haniyeh's leadership was also challenged at times by some Hamas members, who criticised an apparent contradiction between his actions at the diplomatic level and the realities on the ground in the war between Israel and Hamas.
ADVERTISEMENTIn April, Israeli police arrested one of Haniyeh's sisters on suspicion of having ties to members of the movement. A short time later, three of his sons and four of his grandchildren were killed in Israeli airstrikes.