Even his teammates don't know quite what to make out of him sometimes.
David Backes, a teammate of Johnson's in St. Louis and now on Team USA, was talking Thursday about how the lanky 21-year-old looks like a shy, quiet kid at first glance. Yet, that assumption is stone-cold wrong, Backes insists.
"He's always got something to say, and he is probably always lying because he's compulsive and pathological in that area," Backes told NHL.com, throwing out a smile as he dished dirt on his good buddy.
So you can just imagine how confused some of the guys on the American team who don't see Erik Johnson on a regular basis are at times.
All eyes were on Johnson when he scored his first goal of the Olympics during Friday's six-goal first period against Finland in the semifinals.
Pittsburgh defenseman Brooks Orpik plays against St. Louis only once a season, so he had little insider knowledge of Johnson when this team convened in Vancouver two weeks ago. He didn't even know how old Johnson was.
"I didn't know much about him before coming to this tournament," Orpik told NHL.com. "I think everybody has been really impressed with him and the way he handles himself. I don't know exactly how old he is, but he seems more experienced than he is."
Veteran Chris Drury says Johnson is one of the precocious young players on this Team USA that his wife, Rory, sometimes has trouble believing are old enough to be in the Olympics.
"My wife, we get in the elevator at the hotel and she sees them and they leave the elevators and she says, 'That kid is not on your team, he looks like he is 9.' He's on my team and he is one of the best players in the world."
Johnson has the ability to confound on the ice as well.
He is 6-foot-4 and 236 pounds, the biggest "side of beef" -- as GM Brian Burke likes to call his big-bodied players -- on the American roster. Yet he entered this tournament with the reputation as an offense-first player.
"If you talked to people in St. Louis about Eric Johnson is a shutdown role; you might get a few chuckles out of them because he's an offensive guy that has all the tools to put up a ton of points," Backes said.
Johnson has emerged as a shutdown force for the Americans. In Wednesday's quarterfinal against Switzerland, he was on the ice in the last minute of the game as his team tried to protect a 1-0 lead that would deliver Team USA into the medal round.
If you want to know the true worth of a player, just look at how his coach deploys the player. American coach Ron Wilson isn't concerned about preconceived notions. He is in the business of winning -- and he believes that using Johnson as a defensive defenseman is the best expenditure of the youngster's effort.
"That's another thing that these tournaments bring out -- special abilities in players," Backes said. "He's been put it in that role a little bit and he has done a phenomenal job by blocking shots, sticks in lanes and shutting down other guys."
American goalie Ryan Miller has allowed just five goals in four games. But he says his defense has been a big part of that -- and Johnson has been a big part of that, playing more than 17 minutes a game.
"I think everybody has been really impressed with him and the way he handles himself. I don't know exactly how old he is, but he seems more experienced than he is." -- Team USA defenseman Brooks Orpik on Erik Johnson
"I like that he can play a couple different styles," Miller told NHL.com. "He can move the puck or battle with guys in front of the net."
There's the chameleon in Johnson again.
Not surprisingly for such a multi-faceted player, Johnson is quite OK with the mixed messages he delivers with his play.
"I've been trying to do whatever I can to help the team and it has been nice to have the coach be confident in you and put you in those situations," Johnson said. "As a player, you want to be on the ice and be out there when the game is on the line.
"I've really been trying to focus on my defense -- and in short tournaments like this, the details are so crucial. As far as points go, I don't care about that at all, as long as we win."
While Erik Johnson has been opening the eye of teammate and fans alike, Jack Johnson of the Los Angeles Kings, another young defenseman on the U.S. blue line, has been sitting back and watching it all play out with a knowing look.
Jack Johnson might know Erik Johnson better than anybody on this team. The two young men have come up through the ranks together, playing for their country since they were teenagers. They have seen each other in the crucibles of competition that determine the true value of players.
So Jack Johnson is not surprised that Erik Johnson has handled the pressure as if he'd been playing in the NHL for a decade. He is not surprised that Erik Johnson has shown off a solid defense-first game -- and he's not surprised that Erik has fit right into the fabric of this Olympic team.
Jack Johnson has seen it all happen before.
"Erik and I have played in a lot of tournaments like this, so we knew what to expect; but this is obviously the biggest stage most of us have ever played on," Jack Johnson told NHL.com. "We're having fun. We feel honored to be in the Olympic Games and we are just trying to put our best foot forward."