To mark the third fight in the rivalry between Manny Pacquiao and Juan Manuel Marquez on Saturday, every day this week ESPN.com will look back on another memorable boxing trilogy. There have been many in the sport's history, of course, and we don't claim that the five we will review are necessarily the greatest. (If you want one man's version of the best, here is a top-10 list from 2006.) But each of the selected three-bout series has some particular relevance to the Pacquiao-Marquez trilogy that makes it worth celebrating.

Muhammad Ali versus Joe Frazier

March 8, 1971: Madison Square Garden, New York City

Jan. 28, 1974: Madison Square Garden, New York City

Oct. 1, 1975: Araneta Coliseum, Barangay Cubao, Quezon City, Metro Manila, Philippines

There are times when Manny Pacquiao and Juan Manuel Marquez seem to be cordial at worst and are, at best, even friendly. Witness, for example, their "La Bamba" duet on Mexican television recently. It's in keeping with the dispositions of both men, who rarely if ever talk smack about their opponents and who like to emphasize that, as Pacquaio frequently states, "It is business, not personal." And yet, at times, the insistence by Marquez that he should have won both their previous bouts has appeared to aggravate the normally placid Pacquiao, and prompted the Filipino's trainer, Freddie Roach, to suggest that his charge regarded the upcoming contest as more personal than usual.

But nothing either man has said has suggested there is anything like the personal animus that characterized the trilogy between, say, Erik Morales and Marco Antonio Barrera. And it hardly bears mentioning when compared to the friction between combatants in what is widely regarded as the greatest three-fight series ever contested: Joe Frazier versus Muhammad Ali.

Frazier had become heavyweight champion while Ali was in enforced fistic exile following his refusal to be drafted into the military, and Frazier chafed at the fact that Ali continued to be regarded by many as the true champion. He was angered, too -- when Ali returned to the ring and a clash between the two seemed inevitable -- by Ali's insults, taking them personally and not seeing them, as Ali did, as a means to hype their rivalry. By the time they met in the ring, in the third bout of Ali's comeback, the attention and anticipation was like no fight that had gone before it. Burt Lancaster was calling the action for the closed circuit broadcast; Frank Sinatra was a ringside photographer for Life magazine. Frazier was the betting favorite, but Ali led in the early going until Frazier began to take over, ripping Ali with his trademark hooks. He even matched his loquacious foe's taunting:

"God wants you to lose," Ali said during a clinch.

"Tell your God he's in the wrong house tonight," Frazier retorted, resuming his assault.

In the 11th, Frazier hurt Ali badly, and in the 15th he put him down. Ali hauled himself to his feet, but Frazier had retained his crown.

By the time they met again, Frazier had lost the title to George Foreman, but the tension between the two men hadn't eased. Before their second meeting, Frazier and Ali even wound up grappling on the set during an interview with Howard Cosell. But that second fight was a relatively uneventful affair -- as the second fights in trilogies so often are -- that ended in Ali winning a 12-round decision.