PHILADELPHIA — The trip from a strict Pakistani boarding school to a bohemian bar in Philadelphia has defined David Headley’s life, according to those who know the middle-age man at the center of a global terrorism investigation.

Raised by his father in Pakistan as a devout Muslim, Headley arrived back here at 17 to live with his American mother, a former socialite who ran a bar called the Khyber Pass.

Today, Headley is an Islamic fundamentalist who once liked to get high. He has a traditional Pakistani wife, who lives with their children in Chicago, but also an American girlfriend, a makeup artist in New York, according to a relative and friends. Depending on the setting, he alternates between the name he adopted in the United States, David Headley, and the Urdu one he was given at birth, Daood Gilani. Even his eyes — one brown, the other green — hint that he has roots in two places.

Headley, an American citizen, is accused of being the lead operative in a loose-knit group of militants plotting revenge against a Danish newspaper that published cartoons of the Prophet Mohammed. The indictment against him portrays a man who moved easily between different worlds. The profile that has emerged of him since his arrest, however, suggests that Headley felt pulled between two cultures and ultimately gravitated toward an extremist Islamic one.

“Some of us are saying that ‘Terrorism’ is the weapon of the cowardly,” Headley wrote in an e-mail message to his high school classmates last February. “I will say that you may call it barbaric or immoral or cruel, but never cowardly.”

Headley’s e-mail messages, including many that defend beheadings and suicide bombings as heroic, are among the evidence in the government’s case against him and his accused co-conspirator, Tahawwur Hussain Rana, who was born in Pakistan, is a citizen of Canada and runs businesses in Chicago.

The men, who became close friends in a military academy outside Islamabad, were arrested last month in Chicago. They are charged with plotting an attack they labeled the Mickey Mouse Project against Jyllands-Posten, the Danish newspaper whose cartoons had provoked outrage across the Muslim world.

Headley, 49, and Rana, 48, stand out from the young, poor extremists from fundamentalist Islamic schools who strike targets in or close to their homelands. Instead, their privileged backgrounds, extensive travel and bouts of culture shock make them more like Khalid Shaikh Mohammed, the self-proclaimed architect of the Sept. 11 attacks who attended college in the United States, and Mohammed Atta, one of the lead hijackers.

Rana’s father is a former principal of a high school outside Lahore. One of his brothers is a Pakistani military psychiatrist who has written several books, and another is a journalist at a Canadian political newspaper, The Hill Times.

He and his family live in a small brick house on the North Side with a huge satellite dish on the roof. Neighbors described Rana as a recluse who rarely spoke to anyone and whose children never played with others on the street.

“He seemed very committed to his Islamic religion,” said William Rodosky, who once managed Rana’s Halal slaughterhouse in Kinsman, Ill., about 65 miles southwest of Chicago. “He said he wanted the business so he could provide meat to his people and make a little money.”

Rodosky echoed the views of several others who knew and did business with Rana when he said he was “shocked about the terrorism charges.”

The other indicted conspirator, Headley, did not draw the same expressions of shock. Those who knew him paint a more troubled image.

According to family friends in the U.S., the teenager rebelled against his mother’s heavy drinking and multiple sexual relationships by engaging in the same behavior.

“Those were the days when girls, weed and whatever were readily available,” Jay Wilson, who worked at the Khyber Pass, wrote in an e-mail message from England. “Daood was not immune to the pleasures of American adolescence.”

Later, said Lorenzo Lacovara, another former worker at the bar, Gilani began expressing anger at all non-Muslims.

“He would clearly state he had contempt for infidels,” Lacovara said in a telephone interview from New Mexico. “He kept talking about the return of the 14th century, saying Islam was going to take over the world.”