(CNN) -- Ali-Frazier. Leonard-Duran. Gatti-Ward. Zale-Graziano.
Most of boxing's great rivalries produced three memorable fights, trilogies of spectacular action.
They were entertaining fights that demanded sequels, then sequels that demanded sequels.
Rare is the case when it takes a fourth fight to satisfy the fighters, the fans and the press.
Boxers often have other rivals to battle, and younger fighters come along deserving their shots.
But for Manny Pacquiao (54-4-2, 38 KOs) and Juan Manuel Marquez (54-6-1, 39 KOs), their legacies require one more battle in the ring, a fourth fight that will give one a chance to finally hear his name pronounced the winner and a match that could allow the other to push aside the controversial decisions of the past.
That comes Saturday night at the MGM Grand in Las Vegas when the two meet in a non-title fight.
Pacquiao has, in the eyes of the judges, won two of the previous matches. The first was ruled a tie. He believes he won all three. Marquez fervently believes he won all three. Public sentiment and the opinion of sports media fall mostly in the middle.
What everyone agrees on is that the fights have been great. Pacquiao comes hard after Marquez, who counterpunches superbly. Pacquiao has knocked Marquez down four times, three of which came in the first round of the first fight. Had the referee stopped the fight, as they often do after a boxer falls three times, the trilogy would have been a quick one-night stand, or one-night fall, as it were.
Now the two fighters are forever linked.
Marquez, 39, thinks that even though they are fierce rivals now, that might change. He told reporters they might even become friends.
"Because of the great rivalry we had in the ring. I have nothing against him except for the decisions," Marquez, who is Mexican, said, according to an interpreter. "I don't see why we can't have a personal relationship and not just a professional relationship."
But on HBO's 24/7 documentary series, he admits there is some animosity, at least on his part.
"As professionals, we respect each other," Marquez said. "But after everything that's happened, it's starting to get personal. It's heavier. There's more anger. That's how the fourth fight will be."
The soft-spoken Pacquiao, a Filipino legend, always carefully chooses his words.
"I never hate my opponent outside of the ring," he said. "It is just my job to fight, and there is nothing personal. I guess we are kind of friends because I look at all of my opponents as a friend."
Pacquiao's last fight gave him a taste of what Marquez has felt during the reading of the scorecards for their battles. It appeared Pacquiao dominated Timothy Bradley in a 12-round welterweight title fight in June, but he lost the decision on two of the three judges' scorecards.
Naturally everyone predicted a fall rematch, but it didn't materialize. It has a lot to do with money, as Marquez is a better name on the marquee and Saturday's fight stands to draw more viewers to pay per view. According to Yahoo Sports, Pacquiao stands to make at least $8 million guaranteed and as much as $30 million if the pay-per-view sells well. Marquez is guaranteed $3 million, Yahoo reported.
Pacquiao, 33, is more diplomatic about why he is fighting Marquez instead of Bradley.
"I am giving him a chance. I am giving him a chance to prove he can win the fight because he thought he has won all three and he keeps talking about it," he said. "So it is very important to me to win this fight, especially since Marquez really wanted this fight."
Some people have speculated that despite two previous wins, Pacquiao might need a clear victory over Marquez this time to avoid the judges rewarding him for past perceived injustice.
Pacquiao's long-time trainer Freddie Roach has even said that they can't win if they don't get a knockout.
At a press conference announcing the fight, Pacquiao used his thumb to scratch into the tablecloth, "We need to win by knockout" for Roach to see.
"I said, 'Yes, we do,'" Roach said. "That is the best news I've seen yet. Usually it's God will decide or it'll be a close fight or I'm not going to predict anything.
"And the thing is, who is going to give Manny Pacquiao the fourth fight if it's another close call?"
Marquez said he also feels the need to knockout his opponent to clearly win.
He won't change his style, but he said he will fight "with intelligence" and more aggression, Marquez said.
Roach said his fighter will make sure the pace is more up-tempo.
"I think it's going to be a sensational fight. Juan is the most difficult fighter that Manny Pacquiao has ever faced," Marquez's trainer, Nacho Beristain, said.