It’s two a.m., and we’re barreling down a deeply pocked dirt road in Southern Sudan. In the cool of night, the temperature is nearly 100 degrees. Sam Childers, 46, is behind the wheel of a chrome-tinted Mitsubishi truck. Christian rock blares on the speakers. He has a Bible on the dash and a shotgun that he calls his “widow-maker” leaning against his left knee. His top sergeant, Santino Deng, 34, a Dinka tribesman with an anthracite complexion and radiant black eyes, sits in the passenger seat, an AK-47 across his lap. I sit in the back. Since leaving the town of Mundri, headed toward the Congolese border, we’ve been driving for two bone-jarring days on roads littered with the charred wrecks of armored vehicles and fuel tankers, remnants of battles past. A truck follows close behind, carrying 15 men from the small militia group under Childers’s personal command. The convoy is on its way to a Sudanese town called Maridi. In the area we’re passing through, just hours ago soldiers from the Lord’s Resistance Army (L.R.A.) hacked 15 villagers to death with machetes, then disappeared into the bush. Intelligence sources from the Sudan People’s Liberation Army—the ragtag military wing of the breakaway government of Southern Sudan—have indicated that elements of the L.R.A. are now headed to Maridi. Childers wants to intercept them, and kill their leader.

The unflappable Ugandan driving the militia truck wears a torn white pro-life T-shirt emblazoned with a picture of a fetus, a gift from Childers. Most members of his militia are born-again Christians whom Childers has baptized himself. Childers switches from Christian rock to Aerosmith’s “Livin’ on the Edge,” turning up the volume. He’s getting close to his prey. “Let’s do this,” he says. To remove the L.R.A.’s cover, villagers have set fire to the elephant grass on either side of the road. Behind us, the past disappears in a cloud of dust. Ahead, the headlights peer down a fiery tunnel. Sergeant Deng, in the passenger seat, turns around to me and says, “God’s assassins.”

Sam Childers is known in these parts, and back home in Pennsylvania, simply as the Reverend Sam. He is not your typical evangelical Christian missionary, nor, as a white American, is he your typical African warlord. Childers is a former drug dealer and outlaw biker, with tired eyes framed by grizzly muttonchops and a walrus mustache. He claims divine justification for what he does. In firefights, he says, God sometimes tells him when to shoot. He speaks country-singer American, with plenty of grit, and he recounts, over and over, the same stories from his bar-brawling days. He lifts weights, favors army fatigues, and keeps a .44 Magnum tucked in the small of his back. Harley tattoos stretch down his thick arms, and “Freedom Fighter” is airbrushed on the back of his truck. He once owned 15 pit bulls. He seems suited more to bending steel in a motorcycle shop than to saving souls in Sudanese villages.

In 1992, Childers was born again, having promised his wife he would come to Jesus if God granted them a child. A child was born. Leaving behind a life of drugs and crime, Childers set up a hardscrabble church in rural Pennsylvania. In 1998 he used his meager savings to take his first missionary trip to Sudan. He ended up near the border with Uganda, where a complicated and bloody conflict—one of Africa’s so-called forgotten wars—has been raging since 1987. At the center of the fighting is the Lord’s Resistance Army, a guerrilla group led by a Ugandan named Joseph Kony. The L.R.A.’s stated goal is to overthrow the Ugandan government and install a theocratic state based on the Ten Commandments. That effort has entailed systematically ignoring at least one of the commandments, Thou Shalt Not Kill. Most of the others have been breached as well. This forgotten war is the continent’s longest running. It spills across the border from Uganda into Southern Sudan and the Democratic Republic of Congo as the L.R.A. scours the region for conscripts and supplies.