Comrades called him Sergeant Bull. He earned six Bronze Stars, including two for valor in combat. Roadside bombs, firefights, mortar shells whistling down in the night — men he fought with say he faced them with a generous wad of tobacco in his cheek and a laconic confidence they found contagious.

“If there was anyone I wanted to fight beside, it was him; there was none better, and everyone knew it,” one of his commanders in Iraq, Darron Wright, wrote in a book about their 2003 deployment.

Tim Bolyard grew up on a quiet country road in the West Virginia hills, and joined the Army right after high school in 1994. He liked fishing. He liked Metallica. And he liked the Army. As he rose through the enlisted ranks, he read widely and took classes toward a college degree, according to Adam Tymensky, who served with Sergeant Major Bolyard on two deployments to Iraq.

“He was constantly trying to learn, always wanting to better himself,” Mr. Tymensky said. “He never cut corners.”

The meandering strategies of wars that have dragged on for a generation were Sergeant Major Bolyard’s to execute. For much of his adult life, his home was a simple military cot with a photo of his son taped to the wall.

During the invasion of Iraq, Mr. Tymensky said, their scout platoon would often go days without rest: providing security for the battalion commander during the day, and raiding houses at night to search for insurgent fighters. “We’d be dead tired, but if someone needed something, he was right back up again,” he said.

Combat experience made the sergeant major a demanding leader. He rarely raised his voice, men who served under him said, but he pushed them hard to be ready for the worst.