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As New York's police commissioner, Bernard Kerik (search) became known after the Sept. 11 attacks as the fierce, sorrowful face of his reeling department. But the former undercover cop has been confronting danger for decades.

His expertise as a crimefighter and his oversight of the NYPD's heroic efforts during the 2001 terrorist attacks earned him international fame and a role as a special adviser to the Iraqi government, which drew on his help to establish a fledgling police force after the toppling of Saddam Hussein.

Now President Bush, who on Thursday selected Kerik to replace Tom Ridge (search) as secretary of the Homeland Security Department, is counting on him to help defend the nation's borders from terrorist attacks like the one that killed nearly 3,000 people in New York, Washington and Pennsylvania more than three years ago.

When former Mayor Rudolph Giuliani (search) began searching in 2000 for someone to lead the NYPD, he selected Kerik: a fiercely loyal lieutenant who still spoke with the low grumble of a street cop.

About a year after his appointment, Kerik found himself racing to the World Trade Center in lower Manhattan amid reports a plane had struck one of the towers. Soon afterward, as the second plane struck the south tower, sending a shower of rubble and burning debris toward him, Kerik found himself running for his life. He remained stoic alongside Giuliani, who had become "America's mayor" because of his stewardship of the city during the crisis.

More recently in Iraq, Kerik was dubbed the "Baghdad Terminator" after summarily dismissing a newly reinstated Iraqi official who turned out to be a member of Hussein's Baath Party.

Kerik, 49, grew up without knowing his birth mother, a tough kid in Paterson, N.J., where he usually cut classes from the trouble-filled Eastside High School later depicted in the 1989 film "Lean on Me." He learned years later that his mother was a convicted prostitute, possibly killed by a pimp.

Kerik dropped out of high school, getting an equivalency degree, to join the Army, where he became a military policeman stationed in South Korea.

Within a few years, he left the military to work private security in Saudi Arabia, his first taste of the type of security measures used to protect VIPs from terrorists.

After a stint supervising a jail in New Jersey, he became a New York police officer, starting out walking a beat in Times Square when it was still largely the domain of seedy characters and street hustlers. He was promoted to detective and worked undercover busting drug dealers, growing a long ponytail to help him look the part.

In the 1990s, he was tapped to clean up New York's long-troubled jail system. Under his watch as the city's corrections chief, stabbings and fights at the notorious Riker's Island dropped precipitously.

Since leaving the department, Kerik joined Giuliani Partners, becoming a security consultant and then signing on to help launch the Iraqi police force.

During the Republican National Convention this summer, he vociferously backed Bush as the right man to lead the war on terror.

Kerik has two young daughters with his second wife, Halah, and a grown son. He fathered another daughter while stationed in Korea; he was able to find her after Sept. 11 made him a national figure.