You can’t have this conversation without including Nolan Ryan. He’s baseball’s all-time strikeout leader and spent nine seasons with the Astros, more than he spent with any other team. He was part of the club’s first two division winners in 1980 and 1986 and remains the franchise’s all-time leader in strikeouts. His time spent working for the organization after his retirement only adds to his importance.
Looking a bit more recent, we find The Wizard himself, Roy Oswalt. He’s second in club history in wins and strikeouts and third in starts and innings pitched. He was the team’s ace through its playoff runs of 2004 and 2005 despite the presence of Roger Clemens and Andy Pettitte alongside him.
Larry Dierker deserves consideration as both a player and manager. He made his major league debut on his 18th birthday in 1964 and became the team’s first ace. He started the most games and threw the most innings in club history and is third in wins. His years as manager saw the team win division titles in 1997, 1998, 1999 and 2001.
Mike Scott is fourth in club history in wins, and his 1986 season was arguably the best the franchise has seen from a pitcher. He won the NL Cy Young Award and authored a no-hitter to clinch the division title. He dominated the second half of the 1980s.
Joe Niekro has to be on the list by virtue of being the club’s all-time leader in wins and second in starts and innings pitched. He was a big part of that first playoff team in 1980 as well.
Finally, you’ve gotta have arguably the best pitcher in club history, J.R. Richard. He could’ve been a lock for the proverbial Mount Rushmore had a stroke not cut his career short at age 30. Despite that, he’s fifth in club history in wins and third in strikeouts and still holds club records of nine consecutive complete games and three consecutive shutouts.