Philip Rivers will not return to the Los Angeles Chargers for the 2020 season, as the two sides will mutually part ways this offseason, ending a successful 16-year run with the franchise. Rivers, the starting quarterback for the Chargers since 2006, never missed a start with the franchise (his 224 consecutive regular season starts is second-most all-time). He is currently sixth all-time with 59,271 passing yards and sixth in touchdowns (397), and Rivers appears destined for the Hall of Fame when his career ends. Rivers isn't determined to call it a career yet -- he'll sign with another team in free agency this March and likely end his career in another uniform.

Plenty of great quarterbacks have played for another team at the end of their career, some being memorable and others forgettable. Here's a look at 10 best quarterbacks that spent 10-plus years with one franchise before moving on to lead another franchise.

10. Johnny Unitas

Baltimore Colts (1956-1972), San Diego Chargers (1973)

After 17 successful seasons with the Baltimore Colts (winning three NFL titles and a Super Bowl), Baltimore moved on from the league's all-time leading passer and traded the 40-year old Unitas to the San Diego Chargers. San Diego bought in Unitas because they believed Unitas had a few good years left in him and he would mentor rookie quarterback Dan Fouts. Unitas was abysmal in his lone year in San Diego, completing 44.6% of his passes with three touchdowns and seven interceptions in five games (four starts). Unitas was benched after going 2 of 9 for 19 yards with two interceptions in Week 4 and he attempted just one more pass the rest of his career. The Chargers eventually started Fouts in what was the beginning of a Hall of Fame career. Unitas's brief tenure in San Diego was forgettable.

9. Joe Namath

New York Jets (1965-1976), Los Angeles Rams (1977)

Namath tried to get to Los Angeles after several disappointing seasons in New York and years after leading the Jets to a Super Bowl title and the biggest upset in NFL history. After 12 seasons in New York, Namath finally got his wish when he signed with the Rams in the hopes of bringing the franchise that coveted Super Bowl title (the Rams lost three consecutive NFC Championship Games). Namath was brutal for the Rams and so they benched him after just four games when the team got off to a 2-2 start. Namath completed 46.7% of his passes for 606 yards three touchdowns and five interceptions and he was benched after throwing four interceptions in a 24-23 loss to the Chicago Bears. Bothered by chronic knee problems, Namath retired after his lone season with the Rams at age 34 and shifted focus to his acting career.

Baltimore Ravens (2008-2018), Denver Broncos (2019)

Flacco won a Super Bowl in Baltimore and the franchise never had a losing season when he started at least 11 games in any given season. The franchise quarterback who once threw for 11 touchdowns and zero interceptions in the 2012 postseason was replaced in favor of rookie Lamar Jackson after suffering a hip injury during the 2018 season. Jackson led Baltimore to the playoffs and the Ravens traded Flacco to the Denver Broncos the ensuing offseason. Flacco's tenure as Denver's starting quarterback didn't last long, as he completed 65.3% of his passes for 1,822 yards, six touchdowns to five interceptions in eight games. Denver was 2-6 in Flacco's eight starts when he suffered a neck injury and was placed on injured reserve. The Broncos have since moved forward with 2019 second-round draft pick Drew Lock as their quarterback and seem likely to move on from the 35-year old Flacco this offseason.

7. Donovan McNabb

Philadelphia Eagles (1999-2009), Washington Redskins (2010), Minnesota Vikings (2011)

McNabb spent 11 seasons as the winningest quarterback in Eagles history, reaching five NFC Championship Games and making six Pro Bowls. After posting a winning record in 10 seasons as the starting quarterback (and making a Pro Bowl in 2009), the Eagles traded McNabb to the NFC East rival Washington Redskins for a second-round pick. The 34-year old McNabb was a disaster in his lone season with the Redskins, completing 58.3% of his passes for 3,377 yards, 14 touchdowns and 15 interceptions in 13 games. He was benched for Rex Grossman in Week 15 (one month after the team signed McNabb to a five-year extension). The Redskins traded McNabb to the Minnesota Vikings prior to the 2011 season where McNabb was benched after six starts. The Vikings waived McNabb in December of that season and he never played football again.

6. Steve McNair

Houston Oilers/Tennessee Titans (1995-2005), Baltimore Ravens (2006-2007)

McNair led the Titans to Super Bowl 34 (the franchise's lone Super Bowl appearance) and won the 2003 NFL MVP in his 11 seasons with the franchise, but he had a weird divorce on his way out of Tennessee. McNair had to win a grievance against the Titans to be allowed in the facility because the team feared an injury where they would have been stuck with a $23 million cap hit. He was traded to the Baltimore Ravens in June of 2006. McNair still had some good football left and he helped lead the Ravens to a 13-3 record in his first season as the starting quarterback. He threw for 3,050 yards, 16 touchdowns and 12 interceptions and the Ravens had the second-best record in the AFC but ultimately lost in the divisional round of the playoffs. McNair started six games for the Ravens in 2007 before injuries forced the 34-year old to retire.

5. Warren Moon

Houston Oilers (1984-1993), Minnesota Vikings (1994-1996) Seattle Seahawks (1997-1998), Kansas City Chiefs (1999-2000)

Moon may have been 37 when his run with the Oilers ended, but he was in the midst of his sixth consecutive Pro Bowl season when he was traded to the Minnesota Vikings in 1994. Moon made back-to-back Pro Bowls with the Vikings and threw for 4,000 yards in 1994 and 1995. His run with Minnesota ended after he broke his collarbone in 1996, but he would go on to sign with the Seattle Seahawks as a free agent in the offseason. Moon made the Pro Bowl with the Seahawks at 41, throwing for 3,678 yards and 25 touchdowns and he won Pro Bowl MVP honors. He finished his career as a backup for the Kansas City Chiefs before retiring at 44. Moon made three Pro Bowls and threw for 96 touchdowns and 67 interceptions after he left Houston.

4. Randall Cunningham

Philadelphia Eagles (1985-1995), Minnesota Vikings (1997-1999), Dallas Cowboys (2000), Baltimore Ravens (2001)

Cunningham had a successful 11-year run with the Philadelphia Eagles, making three Pro Bowls and winning the Bert Bell Player of the Year award twice. After retiring from football after the 1995 season at the age of 33 (as the league's all-time leading rusher amongst quarterbacks), Cunningham returned to the NFL as a backup to Brad Johnson in 1997. Johnson was lost for the season with a herniated disc and Cunningham shined in relief. He went 13-1 as the Vikings starter in 1998, throwing for 3,704 yards, 39 touchdowns, and 10 interceptions at the age of 35, leading the NFL in passer rating and earning First Team All-Pro honors. Cunningham was benched for Jeff George in 1999 after struggling in the first half of the season and he ended his career with the Dallas Cowboys and Baltimore Ravens. He went 2-0 in both his starts for Baltimore in 2001.

3. Brett Favre

Atlanta Falcons (1991), Green Bay Packers (1992-2007), New York Jets (2008), Minnesota Vikings (2009-2010)

Favre's exit from the Packers after 16 years evolved into one of the wildest narratives in the history of the NFL. The decision came after Favre made a Pro Bowl at the age of 38 and after Green Bay made the NFC Championship Game in that same season. Shortly after announcing his retirement, Favre decided to return that summer. The Packers moved on from Favre and traded him to the New York Jets where he led the league with 22 interceptions but made the Pro Bowl. Shortly after, Favre retired again, only to come back and quarterback the Minnesota Vikings in August of 2009. He had arguably the best season of his career at age 40, completing 68.4% of his passes for 4,202 yards 33 touchdowns to just seven interceptions and a 107.2 passer rating. The Vikings reached the NFC Championship Game as Favre took the eventual Super Bowl champion New Orleans Saints to overtime. Favre played one more season in Minnesota before retiring for good at age 41. He started 321 straight games at quarterback (regular season and postseason) and did not miss a game until his final season.

2. Joe Montana

San Francisco 49ers (1979-1992), Kansas City Chiefs (1993-1994)

Montana's career with the San Francisco 49ers was one of the best in NFL history: Four Super Bowl titles, three First Team All-Pro selections, seven Pro Bowls, two league MVPs. His exit from the 49ers was one of the most controversial in league history, as the team named Steve Young the starter before pivoting and naming Montana the "designated starter" in an attempt to keep him. That didn't work. Montana was traded to the Kansas City Chiefs at age 37 and had immediate success. The Chiefs won their division for the first time in 22 years as Montana threw for 2,144 yards, 13 touchdowns and seven interceptions with an 87.4 passer rating. Montana made the Pro Bowl and Kanas City reached the AFC Championship Game. He played one more year with the Chiefs before retiring after the 1994 season.

Indianapolis Colts (1998-2011), Denver Broncos (2012-2015)

Manning revitalized the Colts franchise in his 13 seasons, winning a Super Bowl and four NFL MVP awards (a league record), leading the league in touchdown passes and passer rating three times. Manning would have finished his career with the Colts if not for severe neck surgery that nearly ended his career. The franchise released Manning at 36 and moved forward with new franchise quarterback Andrew Luck. Manning then signed with the Denver Broncos as the most coveted free agent in history. He led the league in completion percentage in 2012 and earned First Team All-Pro honors. Manning set the NFL record with 55 touchdown passes and 5,477 yards in 2013, winning his fifth NFL MVP award. The next season Manning made his final Pro Bowl before his skills started to diminish in 2015. He still was able to quarterback the Broncos to a Super Bowl title (at age 39) in the final game of his career. In four seasons in Denver, Manning threw for 17,112 yards, 140 touchdowns and 53 interceptions with a 101.7 passer rating. He made the Pro Bowl three times, earned two First Team All-Pro honors while winning league MVP honors and a Super Bowl title. Manning had the best career after spending 10+ seasons with one franchise, cementing himself as one of the top five quarterbacks of all time.