HOUSTON -- The Astros don't have a formula for retiring numbers, which is why they have nine retired numbers and only two players in the Hall of Fame who are wearing an Astros cap on their plaque.

In fact, the Astros haven't retired a number since they retired the No. 5 of Hall of Famers Jeff Bagwell (2007) and the No. 7 of Craig Biggio ('08). Hall of Famer Nolan Ryan (34) also had his number retired, though he has a Rangers cap on his Hall of Fame plaque.

Their other retired numbers include a pair of players who passed away while with the Astros, a successful pitcher-turned-broadcaster-turned-manager and a former National League Cy Young Award winner. Here's a look at the Astros' retired numbers.

Jim Umbricht, RHP: No. 32
Number retired: April 12, 1965
Umbricht played on the franchise's inaugural team, the Colt .45s, in 1962-63 after coming over from the Pirates. The reliever went 4-0 with a 2.01 ERA in 34 games in '62. He was diagnosed with lymphoma during the spring of '63 and returned to pitch later that season, going 4-3 with a 2.61 ERA. His health deteriorated in the offseason and he died at 33 years old on April 8, 1964 -- five days before Houston's season opener.

Don Wilson, RHP: No. 40
Number retired: April 13, 1975
The hard-throwing Wilson made his debut at 21 years old in 1966 and won double-digit games for the Astros in eight consecutive seasons (1967-74), including 16 games twice. In 266 career games with the Astros, including 245 starts, he won 104 games and threw the first no-hitter in a domed stadium on June 18, 1967, whiffing Hank Aaron for the final out. He also no-hit the Reds on May 1, 1969. Wilson tragically died, along with his 5-year-old son, on Jan. 5, 1975, due to carbon-monoxide poisoning in their Houston home.

Jose Cruz, OF: No. 25
Number retired: Oct. 3, 1992
One of the most popular players in franchise history, the left-handed-hitting Puerto Rican played 13 of his 19 Major League seasons with the Astros, earning team Most Valuable Player honors four times (1977, '80, '83, '84) and two All-Star Game nods ('80, '85). When he retired, he was among the franchise's all-time leaders in every significant offensive category, including games, at-bats, runs, hits, doubles, triples, RBIs and extra-base hits.

Mike Scott, RHP: No. 33
Number retired: Oct. 3, 1992
An underachieving pitcher with the Mets at the start of his career, Scott was traded to Houston in 1982 for outfielder Danny Heep and blossomed into one of the most dominant right-handers in the NL. Scott, who discovered a split-finger fastball, went 110-81 with a 3.30 ERA with the Astros from 1983-91, winning the NL Cy Young Award in '86 when he led the Majors in strikeouts (306), innings pitched (275 1/3) and ERA (2.22), and also threw a no-hitter against the Giants to clinch the NL West title. He was the MVP of the 1986 NLCS despite the team losing to the Mets.

Nolan Ryan, RHP: No. 34
Number retired: Sept. 29, 1996
Ryan pitched nine of his 27 Major League seasons for his hometown Astros, throwing his record-setting fifth no-hitter in 1981 and surpassing Walter Johnson as baseball's all-time strikeout king on April 27, 1983. The "Ryan Express" went 106-94 with a 3.13 ERA in 282 career starts with the Astros, making two All-Star teams and winning league ERA titles in '81 (1.69) and '87 (2.76). Ryan finished his career with the Texas Rangers, but became a Texas legend in Houston.

Larry Dierker, RHP: No. 49
Number retired: May 19, 2002
Signed as an amateur free agent by the Colt .45s in 1964, Dierker made his big league debut on Sept. 22, 1964, on his 18th birthday and struck out Willie Mays in the first inning. He became the Astros' first 20-game winner, going 20-13 with a 2.33 ERA in '69, and making the All-Star team. He won 137 games in 13 seasons with the Astros before serving 18 seasons as a team broadcaster and five as the Astros manager, winning four division titles in that span (1997-99, 2001). He was NL Manager of the Year in 1998.

Jimmy Wynn, OF: No. 24
Number retired: June 25, 2005
Dubbed "The Toy Cannon," the 5-foot-9 Wynn was the Astros' first slugger, bashing 291 home runs in his 15-year career, including 223 with the Astros -- a mark that stood as a club record until Jeff Bagwell surpassed him in 1999. Wynn grew up in Cincinnati and signed with the Reds before Houston took him in the expansion draft in 1962. He was the first Astros player to hit three homers in a game and left Houston ranked among franchise leaders in hits (1,291), home runs and RBIs (719).

Jeff Bagwell, 1B: No. 5
Number retired: Aug. 26, 2007
Bagwell was acquired from the Red Sox in a famous midseason trade for Larry Andersen in 1990 before he ever played a game in the Majors, and he never played for anyone other than Houston in his 15-year career. He won National League Rookie of the Year in 1991, MVP in '94, and retired as the franchise leader in home runs (449), RBIs (1,529) and walks (1,401), among other categories. He was eventually inducted into the Baseball Hall of Fame in 2017.

Craig Biggio, C/2B/OF: No. 7
Number retired: Aug. 17, 2008
Biggio played 20 seasons (1988-2007) with the Astros, beginning his career as a Gold Glove catcher before blossoming into a star player at second base. He retired as the franchise leader in games (2,850), at-bats (10,876), runs (1,844), and hits (3,060) and had the most doubles by any right-handed hitter in history (668). He was a seven-time All-Star, won four Gold Gloves and was a five-time Silver Slugger winner. Biggio was inducted into the Baseball Hall of Fame in 2015.

Note: On April 15, 1997, the Astros joined every team in MLB in retiring No. 42 in honor of Jackie Robinson.