Washington first baseman Adam LaRoche signs autographs during spring training. He’s an immensely popular figure across the majors, whether it’s his Nationals teammates or in some cases, fierce rivals. (John McDonnell/The Washington Post)

The morning after he was traded from the Detroit Tigers in early December, Washington Nationals starter Doug Fister already had first baseman Adam LaRoche’s cellphone number, and neither can remember how that happened. The two had rarely crossed paths in their careers except for a brief conversation at first base last season. Fister has spent his five-year career in the American League with the Seattle Mariners and Tigers, and LaRoche has spent nearly all of his career in the National League.

Yet, the Nationals’ social butterfly and one of the most well-liked players in baseball, had already gotten in touch with the team’s biggest offseason acquisition, welcomed him to Washington and told him what to expect from his new surroundings. “Just letting him know that guys are great and everybody is fired up,” LaRoche said.

“He’s just a good dude,” Fister said recently, appreciative of LaRoche reaching out. “A really good guy.”

LaRoche, 34, who is entering his fourth and potentially final year in Washington and hopes to bounce back from a down 2013 season, may not have the unique and fiery leadership of outfielder Jayson Werth or the team spokesman qualities of shortstop Ian Desmond, but his impact is understated. Because he has played for five teams in his 10-year career, he has crossed paths with a lot of players. And because of his laid-back, folksy and funny demeanor, the native Kansan has become friends with everyone from country music singers to reality television stars to baseball players he has never played with.

“A lot of country music stars like to hunt and fish,” said Atlanta Braves second baseman Dan Uggla, never a teammate of LaRoche’s but a friend through his brother. “And Adam likes to hunt and fish. Adam’s got ranches, so do country music stars. Those guys want to be athletes and we want to be rock stars. It’s a good fit.”

“I don’t know if it’s necessarily a good thing if you know everyone in the league because that means you’ve bounced around through a lot of teams, get traded quite a bit and sign with new clubs,” LaRoche added. “But on the other hand, it’s been awesome. I’ve made a lot of close friends and not just guys that I’ve spent the most time with. Guys I’ve run into and hit it off and have a lot in common with.”

Before free agent outfielder Nate McLouth signed with the Nationals this winter, he had all but made up his mind about coming to Washington. But he wanted to check with his friend LaRoche to be sure. The two were teammates in Pittsburgh from 2007 to mid-2009 and Atlanta in late 2009. So the two spoke by phone and McLouth agreed to two-year, $10.75 million deal to join the Nationals as a fourth outfielder.

In recent seasons, baseball has lost some of its biggest and most gregarious personalities to retirement. LaRoche may now be one of the most popular players in major league baseball. During batting practice before every game, he is just as likely to be found hugging and yukking it up with opposing coaches and players as his own teammates.

“He knows everyone,” McLouth said. “I don’t get it either. He’s just a really good teammate.”

Because of his position, LaRoche has gotten to know many players. First base is the most-visited base on the diamond and LaRoche can chat with players about life, baseball, hunting and music. “I get a chance to talk to a lot of guys I’m not going to see very often,” he said. “I’ve gotten to know a lot of people that way.”

LaRoche credits his parents for teaching him to maintain an even-keeled demeanor with everyone whether they are a superstar or clubhouse assistant. But a reason LaRoche can connect with many players is because he has many of the same interests as them: country music, hanging out, fishing, hunting and golf. “A lot of ties back to hunting or shooting of some sort,” he said.

LaRoche even became friends with country singers Jason Aldean and Luke Bryan through hunting. Early in his career, Aldean sang the national anthem before a Braves game in 2004, then he and LaRoche exchanged numbers. LaRoche developed a friendship with Bryan before he had a record deal when he sang at bars in Atlanta.

Now, both singers teamed up with LaRoche and his two brothers, along with Duck Dynasty star Willie Robertson, to open a steakhouse in Steamboat Springs, Colo. The beef comes from LaRoche’s ranch, called the E3 Ranch in Fort Scott, Kan. Bryan even wears E3 Ranch hats in his music videos. And LaRoche is also a partner with them in hunting company and show Buck Commander. The celebrities are occasional guests of LaRoche in the Nationals’ clubhouse and at games.

But because LaRoche considers himself a people person, he also makes an effort to spend time with players who don’t share the same interests as him. Throughout the season, he invites players out to dinner that he doesn’t know well. Two years ago, for example, LaRoche asked to hang out with newly acquired starter Gio Gonzalez, a Miami-area native with a distinctly different background than him.

“If you show somebody that you care about them and you want to get to know them, it usually starts a good relationship,” LaRoche said. “As bad as I was [earlier in life], I always had a soft spot for people. If I knew something was going on with somebody, I love going through it with them, sitting with them one on one. A lot of it is religion-based, too. I’m a big believer in that we’re put here to do more than just play baseball. This going to come and go real quick and we’ll have these relationships long after baseball is over.”

LaRoche is also close friends with fierce rivals. When San Francisco Giants starter Tim Hudson was on the Braves and the team came to play in Washington, he and his family would stay at LaRoche’s house and grab lunch before games. When the St. Louis Cardinals and Nationals play during the season, close pal and starter Adam Wainwright and LaRoche also stay at each other’s houses.

Old-time baseball players like Frank Robinson, who was known to say he didn’t care if he made friends on the field, may frown upon LaRoche’s friendliness with opponents. Rarely enforced rule 3.09 of the MLB rule book actually forbids players of opposing teams from fraternizing “at any time while in uniform.” LaRoche knows he is a frequent offender of this rule, but doesn’t let his friendships with everyone affect him on the field.

“You look back at some old pictures and you see Mickey Mantle before a game taking pictures with two or three guys from the other team,” he said. “I don’t think back then it was an all-out war. I think it’s definitely gotten more lax as time has gone on. I don’t know why. I don’t know if it’s a lot more trades now, guys bouncing around a lot more. But there’s a fine line and out of respect for my teammates and manager, when the game starts, that’s not the time to — I don’t want to say not be friendly — but you save that stuff, the hugs and conversation, you save that until after the game.”