A review of Mr. Johnson's rise and his history, undertaken after he emerged as perhaps the man closest to the state's chief executive, shows that he was twice arrested on felony drug charges as a teenager, including a charge of selling cocaine to an undercover officer in Harlem.

The examination of his background, based on interviews and records, shows he has at least one other arrest, for misdemeanor assault in the 1990s, although there is very little publicly available about that case.

In a statement, Mr. Paterson noted how long ago the drug arrests had happened. "David Johnson has demonstrated, over the course of his adult life, that people can change their personal circumstances and achieve success when given a second chance," he said. "I will not turn my back on someone because of mistakes made as a teenager."

Mr. Johnson, 37, has also on three occasions been involved in altercations with women, two of which led to calls to the police. As recently as October, the police responded to a complaint of harassment at a Bronx address of a woman involved with him. It is unclear if the altercation was verbal or physical or both, but the case is listed as closed.

In 2001, when Mr. Paterson was a state senator, Mr. Johnson, according to a person who was present, punched a girlfriend outside the senator's Harlem office. No arrest resulted, and Mr. Johnson, through a spokesman for the governor, said that he never touched the woman, that she had come to the office inappropriately and that she had been asked to leave by others. He declined recent requests for interviews.

The woman involved, who insisted on anonymity, said in a recent interview that Mr. Johnson had gotten violent with her in the episode. She said she did not file a formal report, but said she had filed an earlier domestic violence complaint to the police about Mr. Johnson. She declined to offer evidence of that.

A spokesman for Mr. Paterson said Mr. Johnson underwent a standard background check by the State Police in 2008, which found no criminal record. Regarding the October incident, the spokesman, Peter E. Kauffmann, said, "The governor looked into the matter, and the complaint has been withdrawn." He said Mr. Paterson planned no further inquiry into Mr. Johnson's history.

Mr. Paterson has made domestic violence a key issue in his career; when he was lieutenant governor, it was among his signature causes. In 2008, just a few months after taking office as governor, he signed a major expansion of New York's domestic violence law to allow judges to issue civil protection orders against people in dating relationships, in addition to those who are married.

Last October, two weeks before the episode involving Mr. Johnson and the Bronx woman, Mr. Paterson opened a campaign to raise awareness about domestic violence, gathering with advocates for a lighting ceremony at the Empire State Building.

He has also become increasingly vocal in his criticism of former Senator Hiram Monserrate, who was convicted of misdemeanor assault last fall for dragging his companion down the hallway of his apartment building. On Friday, the governor praised the Senate's move to expel Mr. Monserrate and spoke at length about the pressures that victims of domestic violence face from their batterers.

"This seemed like a classic case of a woman who was intimidated, who didn't really understand what her independence could be, and was victimized," he said of the Monserrate case, adding, "The reality is that it's really just a prelude to another attack, in many instances."