Eddie Futch, who trained six heavyweight champions with a firmness and compassion that inspired the confidence of his fighters and whose boxing roots went back to the Joe Louis era of the 1930's, died Wednesday in Las Vegas. He was 90.

Futch was still training champions well into his 80's, retiring in early 1998 at age 86, having helped his fighters dethrone so-called unbeatable champions like Muhammad Ali and Roy Jones Jr.

Yet, in boxing's hurly-burly, in the atmosphere of the fast talkers and loud-mouthed promoters, Futch was a quiet, confident little man who had gained his knowledge of the sport from the inside, having started his career as a lightweight in Detroit.

He was definite in his attitude toward his fighters. He worked on mind as well as body, and if a fighter wanted Futch as his trainer, the fighter had to listen. Futch took on the erratic Riddick Bowe after extracting a promise that Bowe would train hard and listen to him. Bowe was known as a laggard in the amateur ranks, a big, bruising belter who softened when anyone stood up to him. When Bowe, favored to win, took the silver at the 1988 Olympics in Seoul, South Korea, his future appeared shaky.

''This boy has been misunderstood,'' Futch said. He took Bowe under his wing, taught him responsibility and dedication, wheedled and cajoled him and helped Bowe win the world heavyweight title in 1992. Then, he dropped him in 1996 when Bowe stopped listening.

Their association was typical of Futch's relationship with his fighters. He mixed compassion with tough love. When Trevor Berbick did not want to sacrifice himself to training after he became heavyweight champion in 1986, Futch walked away from him.

Eddie Futch was born in Mississippi on Aug. 9, 1911, and grew up in Detroit, where he was a star semipro basketball player before he gravitated to boxing. He remembered ''growing up in the Brewster Center there, when Joe Louis was an amateur and when Sugar Ray Robinson, who was Walker Smith then, was just a little kid hanging around.''

Futch captured the Detroit Golden Gloves lightweight title in 1933 and extended his amateur record to 37-3 before a doctor discovered a heart murmur that ended his six-year career in 1936. By then, Futch was established as a coach. Because of his speed -- and his lack of power -- Futch, who was outweighed by 70 pounds, had also become Louis's favorite sparring partner. The role, Futch once recalled, demanded cunning.

''I had to devise ways and means of not getting killed,'' he said. Futch did it well enough to provide Louis with an elusive target.

''Joe used to tell me, 'If I can hit you, Eddie, I can hit anybody,' '' he said. But one day Louis bashed him with a right hand and sent him through the ropes. Futch reconsidered the wisdom of acting as Louis's rabbit.

During World War II, he worked as a welder at the Ford Motor Company and also hooked up with his first pro contender, Lester Felton, a welterweight.

After training lesser known fighters in Los Angeles, Futch did not achieve his first championship until 1958, when Don Jordan won the welterweight title from Virgil Atkins, typically, after Futch had schooled him on the importance of the left jab.

Also typically, as Futch later told it, after winning the title, Jordan thought he was beyond such mundane advice. ''He wouldn't listen to me,'' Futch said, recalling that in the rematch Jordan abandoned the jab while trying to land a knockout punch with his right.

Futch was in despair until Jordan came back to his corner after an early round and said he thought he had broken his right hand.

''Good,'' Futch replied. ''Now you can win.''

After reverting to the jab and using the wounded right only sporadically, Jordan retained the title.

For all his early promise as a coach, teacher and trainer, it was not until middle age that Futch was able to make a sustained living from boxing. While ring insiders were well aware of Futch's knowledge and skills, he was hardly a mainstream name. Often, he was called in to repair other trainers' mistakes or work with hard-to-handle fighters. Sometimes the call came late. In April 1981, he was called in by Larry Holmes less than two weeks before his successful title defense against Berbick, and later that year he was engaged as Michael Spinks's trainer barely two hours before his victory over the light heavyweight champion Eddie Mustafa Muhammad.

Futch became known outside the fight game when he was well into his 50's and took over the training of Joe Frazier. By the time Futch retired, he had handled Bowe, Frazier, Berbick, Holmes, Ken Norton and Spinks among heavyweight champions. Over all, he trained more than 17 world champions at one time or another.

Futch, who was married twice, is survived by his wife, Eva, and four children.

Some of Futch's fighters were involved in some of the sport's most renowned bouts. Working in Frazier's corner in 1971, in the classic battle at Madison Square Garden against Ali, Futch helped develop the techniques that sent Ali to his first defeat. Two years later, working in Norton's corner, Futch watched as Ali lost only his second bout, again to a Futch-trained opponent.

Futch had noticed that Ali, who was so confident of his quickness that he carried his right hand too wide to parry jabs, was vulnerable to that punch. Frazier knocked down Ali with a classic left hook, and Norton was able to pepper Ali with left jabs.

This giant-slayer ability of Futch's fighters continued into the 90's. Roy Jones Jr., unbeaten and considered the best pound-for-pound fighter in the world, lost a light-heavyweight title fight in 1997 to Montell Griffin on a disqualification.

For all Futch's victories, what may have been his greatest gesture came in defeat, when he refused to allow a half-blinded Frazier, possibly ahead on points despite a 14th-round battering from blows he could not see, to come out for a final round of punishment in his loss to Ali in the Thrilla in Manila in 1975. When Frazier went back to his stool after the 14th round, only three minutes from a possible victory by decision, Futch looked at the eye and said to Frazier, ''I'm going to stop it.''

''No, don't do it,'' Frazier replied. ''I can finish.''

Futch said, ''No, this is the best thing to do.''

Later Futch explained: ''Only three more minutes. I'm not a timekeeper. I'm a handler of fighters.''

Edward Futch