Who was Ismail Haniyeh, the Hamas political leader who was killed in Iran?

Haniyeh had been a part of talks as Israel and Hamas negotiated for an end to the fighting in Gaza and a return to the hostages held by Hamas. U.S. Secretary of State Antony Blinken on Wednesday declined to comment on the assassination or how it may affect those negotiations, saying it was an "enduring imperative to getting a cease-fire, and what I do know is we are going to work at that every day."