As head of the command, which oversees the elite Delta Force and units of the Navy Seals, General McChrystal was based at Fort Bragg, N.C. But he spent much of his time in Iraq commanding secret missions. Most of his operations were conducted at night, but General McChrystal, described nearly universally as a driven workaholic, was up for most of the day as well. His wife and grown son remained back in the United States.

General McChrystal was born Aug. 14, 1954, into a military family. His father, Maj. Gen. Herbert J. McChrystal Jr., served in Germany during the American occupation after World War II and later at the Pentagon. General Stanley McChrystal was the fourth child in a family of five boys and one girl; all of them grew up to serve in the military or marry into it.

“They’re all pretty intense,” said Judy McChrystal, one of General McChrystal’s sisters-in-law, who is married to the eldest child, Herbert J. McChrystal III, a former chaplain at the United States Military Academy at West Point.

General McChrystal graduated from West Point in 1976 and spent the next three decades ascending through conventional and Special Operations command positions as well as taking postings at Harvard and the Council on Foreign Relations. He was a commander of a Green Beret team in 1979 and 1980, and he did several tours in the Army Rangers as a staff officer and a battalion commander, including service in the Persian Gulf war of 1991.

One blot on his otherwise impressive military record occurred in 2007, when a Pentagon investigation into the accidental shooting death in 2004 of Cpl. Pat Tillman by fellow Army Rangers in Afghanistan held General McChrystal accountable for inaccurate information provided by Corporal Tillman’s unit in recommending him for a Silver Star. The information wrongly suggested that Corporal Tillman had been killed by enemy fire.

At the Joint Staff at the Pentagon, where General McChrystal directs the 1,200-member group, he has instituted a daily 6:30 a.m. classified meeting among 25 top officers and, by video, military commanders around the world. In half an hour, the group races through military developments and problems over the past 24 hours.

Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, brought General McChrystal back to Washington to be his director last August, and the physical proximity served General McChrystal well, Defense officials said. In recent weeks, Admiral Mullen recommended General McChrystal to Defense Secretary Robert M. Gates as a replacement for General McKiernan.