While athletes sometimes age right before our eyes, sometimes we forget just how long our favorite coaches have been in their sports.

While a great career for an athlete might last 15 years, some of the best coaches in football, basketball, soccer, baseball, and hockey have been at it for several decades.

As expected, many of them have aged quite a bit during that time. Some look like different people altogether.

Here's what some of the biggest names in coaching looked like when their careers began:

Bill Belichick became the head coach of the Cleveland Browns in 1991, at age 39.

BusinessInsider USA Images

Focus on Sport/Getty Images

Belichick, 66, is going on his 20th season with the New England Patriots.

BusinessInsider USA Images

:Al Bello/Getty

Gregg Popovich was the San Antonio Spurs GM before becoming the head coach in 1996, at age 48.

BusinessInsider USA Images

Michael Caulfield/AP

Now 70, he's been with the Spurs ever since.

BusinessInsider USA Images

Thearon W. Henderson/Getty Images

Mike Krzyzewski was 33 years old when he became the head coach of Duke men's basketball in 1980.

BusinessInsider USA Images

Getty Images

Now 72, "Coach K" is perhaps the most well-known coach in college sports.

BusinessInsider USA Images

Patrick Smith/Getty Images

Joe Maddon was 52 years old when he took over the Tampa Bay Rays in 2006.

BusinessInsider USA Images

Reinhold Matay/AP

Now 65, he's on his fifth season with the Chicago Cubs.

BusinessInsider USA Images

Mark Brown/Getty Images

Nick Saban was hired by Michigan State in 1995 at 44 years old, re-joining the college ranks after four years with the Cleveland Browns.

BusinessInsider USA Images

Roger Hart/AP

Now 67, Saban has become a legendary coach at Alabama over the last 12 years.

BusinessInsider USA Images

Wesley Hitt/Getty Images

Mike Tomlin got the Pittsburgh Steelers job in 2007 when he was 35 years old.

BusinessInsider USA Images

Jason Cohn /Icon SMI/Icon Sport Media/Getty Images

He's been with the Steelers since and is now 47.

BusinessInsider USA Images

Keith Srakocic/AP

Mike D'Antoni became head coach of the Phoenix Suns in 2003 when he was 52.

BusinessInsider USA Images

Roy Dabner/AP

Now 67, D'Antoni is on his third season coaching the Houston Rockets.

BusinessInsider USA Images

Eric Christian Smith/AP

John Tortella took over the Tampa Bay Lightning in 2000, at 42 years old.

BusinessInsider USA Images

Bruce Bennett Studios/Getty Images

Now 60, Tortorella is with the Columbus Blue Jackets and one of hockey's most well-known coaches.

BusinessInsider USA Images

Jeff Vinnick/NHLI/Getty Images

Terry Francona became the Philadelphia Phillies manager in 1997, when he was 38 years old.

BusinessInsider USA Images

Mitchell Layton/Getty Images

Now 60, Francona has been with the Cleveland Indians for seven years.

BusinessInsider USA Images

Brace Hemmelgarn/Minnesota Twins/Getty Images

Pep Guardiola was named FC Barcelona's manager in 2008, when he was 37.

BusinessInsider USA Images

Manu Fernandez/AP

Guardiola is 48 and on his third year with Manchester City.

BusinessInsider USA Images

Dave Thompson/AP

Pete Carroll returned to the NFL in 2010 and became the head coach of the Seattle Seahawks at 59 years old.

BusinessInsider USA Images

Ted S. Warren/AP

Carroll is 67 and still with the Seahawks.

BusinessInsider USA Images

John Froschauer/AP

Doc Rivers was 38 when he got his first job as a head coach, with the Orlando Magic in 1999.

BusinessInsider USA Images

Chris O'Meara/AP

Rivers has coached every year since then, now with the Los Angeles Clippers at 57 years old.

BusinessInsider USA Images

Ringo H.W. Chiu/AP

Barry Trotz was 36 when the Nashville Predators hired him as their head coach in 1998.

BusinessInsider USA Images

Bruce Bennett Studios/Getty Images

Trotz is now 56, in his first year with the New York Islanders.

BusinessInsider USA Images

Kathy Willens/AP

Tom Izzo has been Michigan State basketball's head coach since 1995, when he was 40 years old.

BusinessInsider USA Images

Stephen Dunn/Allsport/Getty Images

25 years later, Izzo is 65 and still with the team.

BusinessInsider USA Images

Patrick Semansky/AP

Jim Harbaugh's first head coaching job was with Stanford in 2007, when he was 43.

BusinessInsider USA Images

David Madison/Getty Images

Now 55, Harbaugh is the head coach of Michigan.

BusinessInsider USA Images

Carlos Osorio/AP

Jurgen Klopp was 34 when he became the manager of Mainz 05 in 2001.

BusinessInsider USA Images

Sandra Behne/Bongarts/Getty Images

Klopp, now 51, has been at Liverpool since 2015.

BusinessInsider USA Images

Jon Super/AP

Ned Yost was 48 when he was hired as the manager of the Milwaukee Brewers in 2003.

BusinessInsider USA Images

Darren Hauck/AP

Yost is now 64 and with the Kansas City Royals.

BusinessInsider USA Images

John Minchillo/AP

John Calipari's first coaching job was at Massachussetts in 1988, when he was just 29.

BusinessInsider USA Images

Jonathan Daniel/Allsport/Getty Images

Calipari, 60, is in his 11th season with Kentucky and has a lifetime deal.

BusinessInsider USA Images

Stephen B. Morton/AP

Andy Reid was 41 when he became head coach of the Philadelphia Eagles in 1999.

BusinessInsider USA Images

Doug Pensinger/Allsport/Getty Images

Now 61, Reid is the head coach of the Kansas City Chiefs.

BusinessInsider USA Images

Ben Margot/AP

Rick Carlisle began his head coaching career in 2001 with the Detroit Pistons when he was 42.

BusinessInsider USA Images

Jeff Kowlasky/AFP/Getty Images

Carlisle is now the second-longest tenured coach in the NBA next to Gregg Popovich, now 59 and in his 11th season with the Dallas Mavericks.

BusinessInsider USA Images

Darren Abate/AP

Mike Babcock was 39 when he became head coach of the Mighty Ducks of Anaheim in 2002.

BusinessInsider USA Images

Jeff Vinnick/Getty Images

Now 55, Babcock has been the head coach of the Toronto Maple Leafs since 2015.

BusinessInsider USA Images

Norm Hall/NHLI/Getty Images

Bruce Bochy was hired as the San Diego Padres manager in 1995, when he was 40.

BusinessInsider USA Images

Stephen Dunn/Allsport/Getty Images

Bochy, 64, has been with the San Francisco Giants since 2007.

BusinessInsider USA Images

Lachlan Cunningham/Getty Images

Roy Williams' first head coaching job was with Kansas in 1988, when he was 38.

BusinessInsider USA Images

Getty Images

Williams is now 70 and has been with UNC for 16 years.

BusinessInsider USA Images

Nell Redmond/AP

Now, check out how some of the NBA's biggest stars have changed...

BusinessInsider USA Images

Kathy Kmonicek/AP

What the NBA's biggest stars looked like when their careers began >

See Also: