PITTSBURGH -- They are baseball royalty, for the most part -- players identified by one name, famous nicknames or something even more familiar. Pops. Maz. Big Poison. The Flying Dutchman. Clemente.

Their numbers are among the nine retired by the Pirates along with Jackie Robinson’s No. 42, which has been retired by every Major League club. Their numbers will never be worn again by a Pittsburgh player, coach or manager. It’s one of the highest honors a professional athlete can receive.

Before we speculate about who might be next, let’s first look back.

Pittsburgh’s National League franchise has a 133-year history, so the fact that it has retired only nine numbers on its own should tell you it’s an exclusive club and a high honor. The last time the team retired a number -- Paul Waner’s No. 11 in 2007, 42 years after his passing -- then-CEO Kevin McClatchy told the Pittsburgh Post-Gazette that ownership felt a need to be cautious and “selective” in those decisions.

• Pirates' all-time retired numbers

They have 10 numbers permanently out of use, and there are only so many to go around. Before Waner and Robinson (an MLB-wide honor in 1997), the Pirates hadn’t retired a number since 1987. That was the year they retired Ralph Kiner’s No. 4 and Bill Mazeroski’s No. 9.

There doesn’t seem to be a formal policy in place, as they haven’t retired all their Hall of Famers’ numbers. Max Carey and Lloyd Waner haven’t been recognized in that regard, for instance. Nor have Jake Beckley and Arky Vaughan, although Vaughan’s case is somewhat complicated by the fact that he wore 21, a number that will forever belong to Roberto Clemente in Pittsburgh.

It could be argued that those players didn’t spend their entire careers with the Pirates like Clemente, Willie Stargell and several others who’ve had their numbers retired here. But neither did Kiner or Paul Waner, who played 15 of his 20 seasons in Pittsburgh. Then there’s a question of worthiness -- how high the bar must be -- when you consider that No. 1 was retired in 1954 for former manager Billy Meyer, who went 317-452 in five seasons at the helm.

For those unfamiliar, here’s a quick review of the numbers retired by the Pirates:

No. 1: Billy Meyer
No. 4: Ralph Kiner
No. 8: Willie Stargell
No. 9: Bill Mazeroski
No. 11: Paul Waner
No. 20: Pie Traynor
No. 21: Roberto Clemente
No. 33: Honus Wagner
No. 40: Danny Murtaugh
No. 42: Jackie Robinson (league-wide)

So, who’s next? Perhaps the Pirates will someday honor Fred Clarke or another one of the Hall of Famers mentioned above. Maybe, as they establish their own team Hall of Fame, they’ll expand the honor by retiring a deserving franchise icon’s number.

Aside from players long since retired, there aren’t many obvious candidates to join that class of 10. Dave Parker’s No. 39 has remained in use, with Chad Kuhl currently wearing it, despite the Cobra’s accomplishments and prominence. Barry Bonds (24) won a pair of NL MVP Awards in Pittsburgh but spent twice as much time with the Giants, who retired his No. 25 by the Bay in 2018 -- perhaps ironically while the Pirates were in town. Eleven players have worn No. 24 since Bonds.

Bonds was an early example of a modern tendency that makes this exercise increasingly difficult, especially for small-market teams: Stars rarely spend their entire careers with one team anymore.

Not so long ago, it might have been easy to imagine the Pirates eventually retiring Andrew McCutchen’s No. 22 jersey, for example. He was the face of the franchise during its 2013-15 renaissance, he won the 2013 NL MVP Award, he’s an exemplary citizen, and he remains among the 15 or so most productive players in franchise history.

Nobody has worn that number since he was traded. One player who had the necessary clout declined to do so out of respect for McCutchen, which is why Chris Archer wears No. 24 with the Pirates.

"His jersey's not retired yet, but I think in the future it will be," Archer said in August 2018. "That is his number.”

Here’s one to consider, though: No. 7.

Nobody has worn that jersey for the Pirates since Alex Presley in 2013, but we’re not thinking about it because of the former outfielder. That number once belonged to Chuck Tanner, the western Pennsylvania native who won 711 games as Pittsburgh’s manager from 1977-85 and led the Bucs to their most recent World Series championship in 1979.

David Freese was assigned No. 7 during his first Spring Training with the Pirates, but quickly changed to No. 23 out of respect for Tanner. If that trend continues and the number remains out of circulation, perhaps the Pirates will someday make it official and place Tanner’s number alongside that of fellow managers Meyer and Murtaugh.