How can Don Mattingly help Bryce Harper? It starts with his star power.

A.J. Preller grew up in New York — Long Island, to be specific — in the ’80s.

Guess which baseball player was his favorite.

“Don Mattingly,” the San Diego Padres president of baseball operations said, never hesitating, a few years ago over the phone. “That was the guy. ‘Hitman’ poster on the wall. I was at the last game of the [1984] season, when he won the batting title over [Dave] Winfield. ’85 MVP; ’84-’85-’86-’87, those were my formative baseball years.

“And he was the guy I grew up with.”

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Preller went on and on, and a generation of fans might as well have nodded in agreement. Because for most of a decade, when baseball could still reasonably call itself America’s pastime, Mattingly was the face of the sport — with a nickname to match.

“Donnie Baseball” captained the most storied franchise in the biggest city and ranked among the best players in the majors. But he also penetrated into pop culture, guesting with David Letterman and getting booted from Mr. Burns’ power-plant softball team on The Simpsons.

And while none of that may mean much to many millennials, it surely does to Bryce Harper, never mind that he was eight days shy of turning 3 in 1995 when Mattingly played his final game.

“Players that came before, we usually don’t think that this generation of players knows as much about us as they should,” Mike Schmidt said recently on Phillies Extra, The Inquirer’s baseball podcast. “Not with Bryce. He’s very informed about the alumni like myself.”

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Indeed, Harper is a baseball obsessive with a respect for the game’s past. He talks with familiarity about the ’70s Reds, his father’s favorite team. He picked No. 7 in youth baseball after hearing about Mickey Mantle. As Dusty Baker once said when he managed Harper in Washington, “He’s as knowledgeable of baseball history as anybody that I’ve had.”

So, although Harper met Mattingly only briefly at the 2017 All-Star Game in Miami and may not be able to recite all the pertinent numbers — .307 average, 222 homers, nine Gold Gloves, six All-Star appearances — it’s a safe bet he appreciates his nearly Hall of Fame-level place in the sport.

And it has been years since Harper played for anyone with those credentials as a player.

That wasn’t the primary reason the Phillies this week finalized a two-year contract with Mattingly to be the bench coach. They wanted another voice in the dugout alongside manager Rob Thomson. Mattingly managed for 12 seasons with the Dodgers and Marlins; at 64, he insists he doesn’t want to do it again.

But Thomson also conceded that Mattingly’s distinguished playing career sets him apart among the Phillies’ coaches. Because Thomson didn’t play in the majors. Caleb Cotham (pitching), Kevin Long (hitting), Bobby Dickerson (infield), and others are well-regarded across the majors, but they played in the big leagues only briefly or not at all.

Mattingly’s career gives him instant credibility among players, especially star players. His impact on Harper could be profound.

By all accounts, Harper is coachable. He confides in Long, with whom he worked in Washington before Philadelphia. He took a crash course at first base from Dickerson in 2023 and learned the position on the fly.

But for a two-time MVP who’s likely headed to the Hall of Fame, the conversations with someone like Mattingly must resonate differently.

Harper’s first two Phillies managers — Gabe Kapler and Joe Girardi — had long playing careers. But he hasn’t played for a manager or coach with Mattingly’s name or stature since Baker with the Nationals in 2017.

Add the fact that Mattingly became an icon at first base, and it would appear that he’s uniquely suited to relate to Harper on multiple levels.

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“If there’s things he wants to talk about from a first-base standpoint, then we can talk about it,” Mattingly said in a video news conference this week. “If there’s things he thinks about at the plate, hitting the lefty or hitting the righty, or a certain style of pitcher, I’m going to be like, ‘Hey, what are you trying to do with this guy? What are you thinking?’ I want to learn, too.”

Mattingly recalled fondly a conversation with Harper and former Reds star Joey Votto at the 2017 All-Star Game. He also marveled, like most baseball observers, at how good Harper already was upon making his major league debut at age 19.

“Watching his development over the years, this cat can go,” Mattingly said. “This is a first-ballot Hall of Famer, hands down.”

(Mattingly and Harper did get into a spring-training rock fight through the media in 2018 over Harper’s criticism of the Marlins’ offseason moves, though eight years is a long time for water to flow under a bridge.)

In Washington, Harper hit it off with Baker, whose long, successful managerial tenure was preceded by 19 major league seasons in which he got nearly 2,000 hits and slugged 242 homers. It was reciprocal. Baker once called Harper “a pretty cool little dude” and said he’s “pretty hip on a lot of fronts.” Harper batted .319 with a 1.008 OPS for Baker in 2017.

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Nearly a decade later, as one of this generation’s biggest baseball stars, Harper figures to find “Donnie Baseball” to be relatable and potentially helpful.

“Well, I think we’ll find out, right?” Mattingly said. “You’ve got to build a relationship first. I’ve seen him from afar; I’ve not seen him from the inside. Listen to him, watch him, and just talk.”

The conversations will begin next month at first base on the spring-training half-field in Clearwater.