Vincent Wincelowicz had a hard confession to make to an aging mobster.

“Bad news is,” he said, “I’m an undercover FBI agent.” The mafioso had two choices: Go to prison or become an informant. Eventually, he chose the latter, but his immediate response was surprising.

“I don’t care, you’re still my friend,” he said.

It was this ability to connect to people that helped Wincelowicz excel during his nine-year career as an undercover FBI agent. He used it to infiltrate crime rings and bust corrupt public officials. Wincelowicz, 68, says it also helps him in his current seasonal profession: stand-in for Santa Claus.

He’s in his 16th season as The Brown Palace Hotel’s in-house St. Nick, where he’ll be making merry this weekend. He also reviews the naughty and nice lists at White Fence Farm in Lakewood.

Wincelowicz grew up on Staten Island in New York City and started his law enforcement career in 1972 as a New York State parole officer. He later earned a master’s degree from John Jay College of Criminal Justice in New York and entered the high-stakes world of undercover federal investigations after graduating. Now, he’s the chairman of the criminology and behavioral and social sciences departments at Regis University.

The FBI gave Wincelowicz three different assignments during his time undercover: white-collar crime, the mafia and — during Rudy Giuliani’s term as the top prosecutor in New York — corruption in state agencies.

“We convicted 239 public officials for bribery,” he said. Wincelowicz posed as a salesman of municipal supplies, selling things such as street signs, chains and snow-plow blades, the latter of which, he said, were a hot commodity in upstate New York.

The officials would ask him to charge their cities extra for some items, or they would simply just take a percentage of the contract.

“They would basically say if you don’t want to do this, somebody else will,” he said. It turned out that other contractors were in on the schemes. “We indicted nine other vendors.”

When he dealt with the mafia, Wincelowicz posed as a “fence,” someone who bought stolen items. One year, he bought truckloads of stolen Cabbage Patch Kids dolls from the mafia in Buffalo, N.Y. Later, when the men were being arrested, one of them asked the agents, “Is this about the dollies?” Wincelowicz recounted.

Back then, the FBI didn’t have the robust undercover program it does now. “We were pretty much flying by the seat of our pants,” he said. Agents were left to figure out a way to get criminals to trust them.

“In the bureau, when you go undercover, you’re gone. You don’t come back to the office, so you have to be good at making relationships. You have to assimilate into that culture,” he said.

Being able to make connections to people and build relationships is essential for undercover work, he said. It’s also vital that an agent’s story lines up.

After he retired from the FBI, Wincelowicz moved to Littleton to pursue a teaching gig. One day, he saw a television commercial for a Santa school and decided it looked fun. He signed up and soon found himself in a classroom with other prospective Santas. They learned things such as the history of Santa Claus and how he gets into people’s homes (through the chimney or with a magic key). Wincelowicz “cut his teeth” as a mall Santa before moving to the posh Brown Palace.

With his natural white beard and 6-foot-tall, hearty build, Wincelowicz is a natural fit for the role. He also does video calls with kids, after being briefed by their parents.

Wincelowicz, Ms. Claus, and their two elves are scheduled to appear at sold-out events at the Brown Palace on Saturday and Sunday, but if you happen to be at the historic hotel to look at the Christmas decorations between 9 a.m. and 1 p.m., you might catch him strolling through the lobby. He also will be on duty 5 to 8 p.m. Saturday at the White Fence Farm in Lakewood.

This year, a common request is for hard-to-find Hatchimals, stuffed animal toys that come in an egg. However, not all of the children wish for toys and video games.

“A lot of the kids ask for stuff you don’t expect. ‘I want people to get along better. I want stuff for my mom and dad,'” he said. “One of the things they always ask me is ‘What do you want for Christmas, Santa?’ I always say, ‘I want you to be happy.’ ”

Part of the job of being Santa Claus is making sure all of the kids feel comfortable and welcome, as the scene can be overwhelming and scary for some. Wincelowicz likes to walk around before the event begins to warm up the crowd.

One year at the Brown Palace, Wincelowicz saw a girl — in a purple velvet dress and adorned with a hat — standing nervously off to the side of the room. Wincelowicz went over and started talking to her and she warmed up.

The girl’s mother approached Wincelowicz later, tears in her eyes. Her daughter had cancer and had been worried about attending the event because she was wearing a hat to cover her hair loss.

“I made that family’s day,” Wincelowicz said. “No script or anything.”