Before we investigate, it is imperative to first establish what separates one player from the next in an Association filled with the world's best athletes.
In this article, James is being specifically compared to a list of legendary athletes who possessed the rarest combinations of size, speed and leaping ability while also dominating multiple phases of the game.
Meaning—besides rising up and dunking on the heads of their defenders—this list is reserved for those athletes who also excelled in the ability to dribble, pass and shoot.
As a 6'8" point guard, for example, Magic Johnson was a great athlete. But despite the long list of things that Johnson could do, he was never a great leaper.
Shawn Kemp, on the other hand, was one of the NBA's greatest leapers ever in his prime. While Kemp excelled as a scorer and rebounder, however, he never averaged more than 2.6 assists in any season.
Johnson, Kemp and others of the like were omitted from the list of comparable athletes below for those reasons.
To determine whether James is or isn't the best athlete the NBA has ever seen, though, Wilt Chamberlain, Oscar Robertson, Julius Erving and Michael Jordan must all be discussed.
Wilt "The Stilt" Chamberlain, NBA Career: 1959-73
During the 1961-62 season with the Philadelphia Warriors, Wilt Chamberlain became the last player in NBA history to average 50 points. He is also the last to average as many as 40 points when he finished the following year at 44.8.
But what's often lost from a career filled with highlights of Chamberlain dominating smaller, less physically gifted athletes than we have in the game today is that he could do much more than simply score.
As a 7'1" center, Chamberlain averaged 8.6 assists during the 1967-68 campaign. He also dished out 4.5 assists or more four other times in his career.
Besides that, though, he also demonstrated a leaping ability that won him the Big Eight high jump competition when he cleared the bar at 6'6" as a junior at Kansas.
Oscar "The Big O" Robertson, NBA Career: 1960-74
Oscar Robertson became the last player in NBA history to average a triple-double. During the 1961-62 campaign, he posted 30.8 points, 12.5 rebounds and 11.4 assists.
His all-around brilliance—that led to averages of 25.7 points, 7.5 rebounds and 9.5 assists for his career—has left Robertson as the player most often compared to LeBron James.
While he played in a different era where dunking was sometimes associated with showing off, Robertson chose not to finish with the same authority that James does now in the spirit of sportsmanship.
As evidenced by this block above, however—one in which Robertson's hand extends to the top of the box on the backboard—he certainly possessed the athleticism to do so if he wanted.
Julius "Dr. J" Erving, NBA Career: 1971-87
Julius Erving left behind a legacy of athletic artistry highlighted by layups like the one above for NBA fans to celebrate forever.
Over a career that spanned five professional seasons with the ABA in combination with 11 more in the NBA, Erving finished with 24.2 points, 8.5 rebounds and 4.2 assists total.
Amid the high-flying brilliance, he also dished out at least four assists nine times in his career. He collected seven or more rebounds nine separate times as well.
Besides being one of the greatest pure athletes the game has ever seen, Erving left a lasting legacy.
Michael "Air" Jordan, NBA Career: 1984-2003
As the greatest player in NBA history, Michael Jordan needs no introduction. In saying as much, though, I do feel like we sometimes forget the type of passer that Jordan was.
While he certainly wasn't Magic Johnson by any means, Jordan did use his extreme athleticism to average eight assists during the 1988-89 season while also grabbing eight rebounds and scoring 32.5 points.
This, in addition to dunking on the heads of people like Patrick Ewing in the video above.
At 6'6", despite not quite having the size and strength of LeBron James, Jordan could beat his defender out of a post-up position just as easily as he could off the dribble.
Jordan used his athletic ability to become one of the best defenders in the game during his era as well, finishing with an average of 6.2 rebounds for his career.
LeBron "King" James, NBA Career: 2003-Present
LeBron James recently became the youngest player ever to score 20,000 points. He is leading the league in player efficiency rating for the sixth straight season and on his way to a fourth MVP.
He is also the greatest athlete that I've ever watched break into the league, though I wasn't old enough to remember Jordan until the mid-'90s.
But in saying as much, I am not prepared to call James the greatest athlete the NBA has ever seen.
From David Thompson to Shaquille O'Neal, and Dominique Wilkins to Vince Carter, James is a better overall athlete than any other NBA great I did not highlight above.
I will also concede that he is a bigger, stronger, faster version of Erving, and he's more physically dominant than Jordan from a strength perspective.
But James has not proven to be as versatile of an athlete as Oscar Robertson, nor does he quite possess the size and athleticism of Chamberlain.
Robertson was a walking triple-double who dominated more phases of the NBA game to a larger degree than James has thus far.
While James is yet to average as many as nine rebounds in any one season, Robertson did so five times. He also dished out more than James' career high of 8.6 assists nine times as well.
The explosiveness, vision and quickness that defined Robertson's game would translate to today's NBA in a similar fashion too—just as Chamberlain's freakish athleticism would.
Chamberlain certainly never matched up with a player the size of O'Neal, for instance, but he could run faster, jump higher and do more things on a basketball court than any athlete we've seen since—including James.
It's close, at the moment, but right now I'd answer the question by ranking James third. Just ahead of Jordan at fourth and Erving fifth, with Robertson and Chamberlain at second and first, respectively.
Until James averages a triple-double like Robertson, or becomes a seven-foot high-jumper like Chamberlain, I don't expect that to change.