The death of the Hamas leader Yahya Sinwar, who was killed on Wednesday by Israeli forces in Gaza, deals a significant blow to the militant organization.

Israel has made eliminating Hamas’s leadership an aim of the war in Gaza, and it considered Mr. Sinwar one of its biggest targets. Long considered by Israel and the United States as the planner of Hamas’s military strategy in Gaza, Mr. Sinwar also took on the role of the organization’s political chief two months ago, after the assassination of Ismail Haniyeh.

For months, Mr. Sinwar had evaded the sort of Israeli efforts to find and kill him that have led to the deaths of other senior officials in Hamas, including Mr. Haniyeh.

Hamas’s leadership structure is opaque, but here is what is known about some of Hamas’s most prominent figures who are still believed to be alive or whose fate is unclear:

Khaled Meshal, a former political head of Hamas

Born near the West Bank city of Ramallah, Mr. Meshal became the leader of Hamas’s political office in 1996, directing the group from exile. Two years later, Israeli agents injected him with a slow-acting poison in Jordan, sending him into a coma before he was saved by an antidote provided by Israel as part of a diplomatic deal with Jordan.

Mr. Meshal spent his career moving from one Arab nation to another, living in Kuwait, Jordan, Qatar and Syria. When he stepped down as head of the political office, he was succeeded in 2017 by Mr. Haniyeh. Mr. Meshal remains an influential official in the group.