When he was in his 20s and teaching high school history at Bishop Kenrick in Norristown, Joseph Clancy decided to put on a suit, make his way into the city, and head to the Secret Service field office at Sixth and Arch Streets.

Clancy, a Havertown kid, had wanted to be in the Secret Service since John F. Kennedy was killed, which he figured he could tell someone at the office. Even if there wasn't a job opening, Clancy - an Archbishop Carroll and Villanova graduate - thought maybe he could persuade someone to let him join.

Eventually he succeeded.

Eventually.

"By the fifth year," Clancy recalled last week, "they finally realized, 'This guy is pretty persistent.' "

Clancy, 60, three decades removed from his in-person cold-calling days, is now director of the U.S. Secret Service, the top official at the 6,400-employee agency that will oversee security at this week's Democratic National Convention.

During an interview from Cleveland last week, where Clancy was overseeing the final day of the Republican convention, the director discussed his Philadelphia roots, his 27-year career at the agency - where he once led President Obama's security detail - and the challenges of managing a convention in his hometown.

Handling those challenges will take up most of his time while he's here this week, but Clancy still said he's excited for a few rare moments where he can enjoy the benefits of being home (he's scheduled to meet up with at least one childhood friend).

"I love Philadelphia," he said, "so it is always a great feeling to come back."

Clancy grew up in Delaware County, went to grade school at St. Denis in Havertown, and played football in high school at Archbishop Carroll, where the Patriots won the city championship in 1971.

After graduating in 1973, Clancy enrolled at West Point, but he struggled with academics and later transferred to Villanova, which he said was a "perfect fit."

After college, Clancy took up teaching, first at Bishop Kenrick for four years, then for a year at Father Judge High School.

But his eye had been focused on the Secret Service since childhood, when he remembered watching for days on television as people mourned Kennedy's assassination.

"Even at that age I thought [protecting the president] was an important mission," Clancy said.

After successfully badgering his way into the Secret Service in the Philadelphia field office in 1984, Clancy spent decades working his way up the ranks, bouncing from his hometown to presidential protection details and other Secret Service offices across the country, including New York and Washington.

He also married and had four children. His wife, Andrea, from Drexel Hill, has extensive ties to the region as well: Her father worked at Villanova for 33 years, and her brother, Harry Dietzler, is executive director of the Upper Darby Summer Stage, which counts Tina Fey as one of its many alumni.

In 2009, Clancy was selected to head Obama's security detail, a position he held until retiring in 2012 to take a corporate security position with Comcast. Clancy traveled to more than 80 countries with the president, he said during a speech last year at Villanova, and he can be seen in the margins of scores of photos from Obama's first term.

Clancy returned to head the agency in 2014 at the request of the president after it endured a series of embarrassing scandals. He was named the permanent director in February of last year.

Since then, Clancy has overseen several big events, he said, including the pope's visit to Philadelphia in September. He's confident that the blueprint the agency uses for such spectacles - deployed at least 50 times over the last two decades, according to Clancy - can be a success again here, particularly because the plan has been customized for this convention and intensely reviewed for months.

Still, Clancy said he prefers to focus on the specific tasks rather than making big, bold predictions.

It's the quality that perhaps best describes why he never imagined going from a walk-in hire to leading the agency one day.

"I was really focused on day-to-day operations . . . think that carries over today," he said. "I've never really looked too far ahead."

cpalmer@phillynews.com

215-854-2817@cs_palmer