Akhenaten.
People mostly remember him for being a religious nutcase who pissed off the Egyptian political establishment so much they pulled a He Who Must Not Be Named with him in the historical record, but there was another side to his insanity. For one, he had no foreign policy. Okay, that's not quite true, but it sure seems like it at times. To give one example, when the Amorites besieged the city of Byblos, an important vassal in northern Lebanon, the city sent at least 60 letters to Akhenaten pleading for him to send an army to lift the siege, and only surrendered when Akhenaten sent back an irritated letter telling them to stop bothering him. The Amorites, who had been Egyptian vassals themselves, then defected to the Hittites and Akhenaten did nothing about it. He also did nothing to save the Mitanni, his father's biggest ally, when the Hittites went after them. At absolute most, Akhenaten only ever sent limited forces to aid his vassals (in the event that he decided to aid them at all), whereas his predecessors' policy had always been to personally lead a large punitive army against the transgressor.
Thus, many of Egypt's vassals in Canaan abandoned it over the course of Akhenaten's reign, and the Hittites were allowed to become stronger without any effective opposition. Had Akhenaten presented a stronger stance in Canaan, as his predecessors had done, he could have saved his successors much trouble in trying to fix his mess.