Lou Gehrig
Donald Campbell (whild going for a world water speed record, his boat, the Bluebird, crashed and disintegrated. They never found the body.)
Ed Delahanty (the defending AL batting champ, and hitting .333 when he died after getting drunk and falling over Niagara Falls).
O. G. “Collie” Smith, cricketer for Jamaica/West Indies, who died in a car crash while on tour in England. At the time, many considered him to be as good a batsman as his teammate Garry Sobers (who ironically was also in the car Smith was in). Sobers went on to be one of the three best batsmen of all time.
Does Nelson Rockefeller count? 
Vladimir Konstantinov - he wasn’t killed, but he suffered brain damage, and will never walk again after a limo accident a few days after the Red Wings won the Stanley Cup.
Trent Kresse, Scott Kruger, Chris Mantyka, Brent Ruff - members of the WHL (junior hockey) Swift Current Broncos who were killed in a bus crash en route to a game. Ruff was the brother of current Buffalo Sabres coach Lindy Ruff. Who knows what might have happened to their careers - on the bus were future NHL’ers Joe Sakic and Sheldon Kennedy.
Bill Barilko - Scored the Stanley Cup winning goal for the Leafs in 1951. That summer, his plane crashed in north Ontario. He was immortalized in the Tragically Hip song, 50 Mission Cap.
Bill Masterson, hockey player. Died of head injuries suffered in a game. I’m 99% sure he wasn’t wearing a helmet. The Masterson Award is named after him, given annually to the player best displaying perserverance. Tony Granato won this once after coming back from brain surgery to play again.
Oh, and let us not forget Tim Horton, Maple Leafs defenseman who was killed in a car crash. The donut chain is named after him.
Also George Gipp “The Gipper” died of pnumonia (I think) while still one of the great college football players at Notre Dame.
Hard to believe that someone [cough, cough] hasn’t already submitted this one:
Ruffian
Kurt Bevacqua
Hey, some of us are sick, just got in a car accident, and are having their bridal shower this weekend. We’re in a new dimension of busy-ness.
That said…I’ll add other pertinent equines to the list:
**Landaluce ** (filly; succumbed to illness)
**Go For Wand ** (filly; broke down in the ugliest way I’ve ever seen)
Swale (colt; died from illness not long after his Kentucky Derby and Belmont wins)
Phar Lap (colt; died from illness)
And non-equines…to return to the car-racing scene:
Scott Brayton
He was a long-time friend of the family; my dad used to work pit crew for him; we went to his wedding. He died five years ago, after securing the Pole for the Indy 500, in what should have been a routine test drive around the track.
Not sure if this will count, but I seem to recall that Hall of Famer Christy Mathewson had his career prematurely ended by expsoure to Mustard Gas in WWI. It was eventually a fatal condition.
Also, what was the basketball player’s name that died of a heart attack while in practice. If I recall correctly his death was rumored (erroneously) to be cocaine related.
Ruffian, were any of those horses the one that broke its leg in the Breeder’s Cup sprint about 10 years ago? I still consider that to be the ugliest sports injury I’ve ever seen, and I watch football on a religious basis.
beakerxf, I think the basketball player you’re talking about was Len Bias.
Re: the OP, Rocky Marciano was the only heavyweight boxer to ever go undefeated in his career, IIRC. Seems that he died in a plane crash, but I could be wrong.
If I’m not to be mistaken didn’t track star Florence Joyner (“Flojo”) die at an early age of few years back? Or am I mistaking her for somebody else entirely?
More good names, though I don’t consider horses athletes. However, to quibble would be in direct conflict with my OP.
Lou Gehrig and Christy Matthewson are good names.
I think the Gipper was made legendary by his death rather than dying as a legend, but a good addition too.
I’ll also add the non-legendary Bo Diaz.
So far, I’d say that true legends that died while on top (or at least while active or contracted a deadly illness that caused them to leave the sport and pass on shortly afterward)) were:
<B>DALE EARNHARDT
ROBERTO CLEMENTE
RIKIDOZAN
LOU GEHRIG
CHRISTY MATHEWSON
PAYNE STEWART
TERRY SAWCHUCK
HOWIE MORENZ
FRANK GOTCH
O.G. SMITH
SWALE
FLORENCE JOYNER
Any more condidates? What about soccer players and boxers?
I managed to remember his first name. I think it was Reggie (Lewis?). I think he was a Celtic.
Yes and no. Breeder’s Cup, yes, Sprint, no. Go For Wand broke down in the 1990 Breeder’s Cup Distaff while engaged in a heated near match-race with Bayakoa, her leg shattering maybe 100 yards from the wire. It was so severe that she actually did a forward roll. Her leg was just dangling afterwards–literally the only thing holding it on afterwards was the skin. NBC cut to commercial, and when they came back, the filly was dead. Sports Illustrated had the great taste ( :rolleyes: ) to do a frame-by-frame photo spread of her break down, in addition to several shots of her hobbling about on three legs–and even one of her receiving the lethal injection.
Interestingly enough, there was an equine fatality–two, actually–in the BC Sprint that same day. On the far turn, Mr. Nickerson had a heart attack and kind of leaped into the air in a death lunge. Shaker Knit, who was behind him, was unable to avoid the fallen horse and tripped over him. He landed on his back, breaking it and instantly paralyzing him. He was put down.
1990 was an ugly, ugly year for racing. I seriously couldn’t stomach the sport for several years after that.
There is another horse that broke down in the BC Sprint, however…Mr. Brooks broke down in the same place–far turn entering the stretch–in the 1992 running of the event. As both this and the other Sprint fatalities occurred on the vision-obscurring far turn, I’m wondering if you’re remembering Go For Wand’s gruesome demise. Which of these strikes a chord?
Vinnie, if I may say so, Ruffian belongs up there with Swale as the top two of the five horses mentioned. She was a blistering freak of nature, and died during a break down in a match race with that year’s Derby winner. In her lifetime (prior to the fateful match race, of course), she never lost, nor was she ever even headed. She set track records like they had been set by fat shetland ponies, and European publications placed her in the top 10 horses of the past century–nearly a dozen places ahead of Man O War.
Just my thoughts.
Yes, it was Boston Celtic Reggie Lewis.
The OP suggests “while they were on top”. I think this means that, who was at or near their prime when death came.
By that criteria, this is my list.
Thurman Munson, an all-star catcher.
Reggie Lewis, an NBA rising star.
Hank Gathers, an NCAA All american and certain lottery pick in the NBA draft.
Payne Stewart, just won his second US Open.
Greg Moore, a top Indy car driver.
Len Bias, U of Maryland All american and the second overall pick in the NBA draft, by the Celtics.
Derrick Thomas, perrenial Pro Bowl linebacker for the Kansas City Chiefs.
NASCAR’s Davey Allison, Alan Kulwicki were rising stars, Adam Petty was but 19 years old with much potential.
And 7 time Winston Cup champion Dale Earnhart, who was at the top for all of 21 years in Winston Cup, finishing second in the points just last year.
They all died too soon, and all had a good chance to continue to be at the top of their game.
There are others,but I’m not a follower of horse racing and don’t know hockey all that well.
Ray Chapman of the Cleveland Indians would probably have made the Hall of Fame if he didn’t die (at least in Bill James’s opinion). Chapman died in 1920 as a result of being hit in the head by a pitch.