Yahya Sinwar, the leader of Hamas has long been viewed as one of the militant group’s most influential leaders, wielding outsize power while remaining mostly hidden in tunnels beneath Gaza.

Israel’s military said on Thursday that it was examining the possibility that he had been killed in Gaza — a prospect that, if confirmed, would raise hopes of an end to the conflict.

Long considered a planner of Hamas’s military strategy in Gaza, Mr. Sinwar consolidated his power when he was chosen in August to lead the group’s political office as well. He was elevated to that post after the assassination of the group’s political chief, Ismail Haniyeh.

Here’s what we know about Mr. Sinwar and his past.

Formative years

Mr. Sinwar was born in Gaza in 1962 to a family that had fled its home, along with several hundred thousand other Palestinian Arabs who fled or were forced to flee during the wars surrounding the creation of the state of Israel. This displacement deeply influenced his decision to join Hamas in the 1980s.

Mr. Sinwar had been recruited by Hamas’s founder, Sheik Ahmed Yassin, who made him chief of an internal security unit known as Al Majd. His job was to find and punish those suspected of violating Islamic morality laws or cooperating with the Israeli occupiers, a position that eventually landed him in trouble with Israeli authorities.

A crucible

Mr. Sinwar was imprisoned in 1988 for murdering four Palestinians whom he accused of apostasy or collaborating with Israel, according to Israeli court records. He spent more than two decades in prison in Israel, where he learned Hebrew and developed an understanding of Israeli culture and society.