The "Core Four" are former New York Yankees baseball players Derek Jeter, Andy Pettitte, Jorge Posada, and Mariano Rivera.

Each member of the Core Four was a key contributor to the Yankees' late-1990s and early 2000s dynasty that won four World Series championships in five years, and a fifth in 2009.

Three members of the Core Four—Jeter, Rivera and Posada—played together for 17 consecutive years (1995–2011),[1] longer than any other similar group in the history of North American professional sports.

Derek Jeter, Mariano Rivera, Jorge Posada, and Andy Pettitte all joined the New York Yankees organization in the early 1990s as amateurs.

[10] The latter threw a knuckleball at the time, which Posada struggled to catch (hitting him mostly on the knee), prompting Pettitte to abandon the pitch.

[10] Promoted to the Greensboro Hornets of the Class A South Atlantic League in 1992, Posada and Pettitte met Jeter, a highly regarded prospect, who had been assigned to the team.

[10][15] Posada made his major league debut in September, and along with Pettitte and Rivera, was included on the Division Series roster.

[4] That season, Jeter, Pettitte and Rivera won their first championship together (Posada was left off that year's postseason roster).

[23] Jeter's third milestone in 2011 was breaking Mickey Mantle's record for most games played as a Yankee, accomplishing this on August 28, 2011 against the Orioles.

[28][29] He was named the 2001 American League Championship Series Most Valuable Player[30][31] and won the Warren Spahn Award in 2003 as the best left-handed pitcher in baseball.

[56] In 2010, Rivera, Jeter, and Posada became the first trio in any of the four North American major sports leagues to play together on the same team for 16 consecutive seasons.

This broke the record for most regular-season games played together by two Yankee teammates, previously held by Lou Gehrig and Tony Lazzeri.

[58] With the rise of free agency and trades, many sportswriters believe that it is highly unlikely that another group of players of comparable size will spend their entire careers with a single team.

[59][60] Buck Showalter, the Yankees manager during the Core Four's major league debuts in 1995, said, "[Y]ou won't see anything like this happen again.

"[15] Pettitte was the first player of the Core Four to retire, announcing his decision at a news conference at Yankee Stadium on February 4, 2011.

He told the organization "not to count on his return" after the Yankees lost the 2010 American League Championship Series to the Texas Rangers, citing his desire to spend more time with his family.

[62] However, he reversed his decision on his final day as instructor and rejoined the organization on March 16, signing a $2.5 million minor league contract.

"[73][74] He intended to reveal his decision at the end of the year, preferring a low-key departure instead of having a farewell tour across MLB stadiums.

[75] However, he reversed his decision after tearing his anterior cruciate ligament (ACL) and part of his meniscus while shagging fly balls on May 3, 2012.

[79] His farewell tour saw him meet the fans and unsung employees of opposing teams during his final visit to their ballparks to listen to their stories and thank them for supporting baseball.