ath·lete [ath-leet]
–noun a person trained or gifted in exercises or contests involving physical agility, stamina, or strength; a participant in a sport, exercise, or game requiring physical skill.
There is NO way to state who is the greatest athlete - it is not apples to apples. Swimming vs baseball vs track vs etc vs etc
There has to be common ground other than just being an athlete. You can call someone the greatest Olympian (based upon medals earned) or the greatest swimmer, greatest baseball player, etc but the common ground is missing to link sports.
Tiger, he is an athletic golfer, as opposed to some of those that need a 'bro' or 'manzere'. He had transformed the sport as well, many do what it takes to try to keep up.
Some will say baseball is not an athletic sport BUT take in account the toll it can take on a body. 162 games a year plus travel. Sure games are only about 3 hours a day but add in pre-game & post game activities, it is a full day of work. If you are a pitcher you get 20-35 or so starts per year - throwing >100 pitches. It takes a toll on the whole body. Yes you can look like David Wells but there is an inner athlete there somewhere. As far as hitting a baseball that can vary from 60-103 mph, bending, dipping, curving, splitting - it is THE most difficult skill to master in sports. Hence why you can fail 7 out of 10 times and be paid millions, be an All-Star and called one of the best ever.
Many go for multi-sport stars and believe that is what could make them the best ever. Cannot tell as some who went down one path and stayed there never showed what they could do in another sport.
Michael Jordan learned that baseball was not as easy as he thought (or was he on hiatus from the NBA because David Stern told him to take a few years off?)
Danny Ainge baseball/hoop - better career in hoop
Bo Jackson - serious talent is too sports - injury took him down to early
Dave Winfield - drafted in 3 if not 4 pro sports
Jeffrey Alan Samardzija - football at ND, gave it up to play baseball, now closing for the Cubs
Charlie Ward - football/hoop
Bob Hayes - football/track
Deion Sanders - football/baseball & you can say track, he ran in college
.......that's probably enough about nothing........