Who I think should be considered:
Artis Gilmore
Played five season with the Spurs. Averaged 16.1 points, 9.7 rebounds and 1.8 blocks over those five seasons. Shot 62.1% from the field while with the Spurs. Two-time NBA All-Star with the Spurs.
Bob Bass
Was the GM of the Spurs from 1974-75 to 1993-94. Filled in as interim coach four different times. Did a very good job of helping the Spurs remain a winning franchise while being given limited funds by the owners he worked for. In his 19 seasons as GM, the Spurs were a combined 894-750. The Spurs were at or above .500 in 14 out of the 19 years he was GM. As a coach, his all-time record was 143-108 (5th most coaching wins in franchise history, 6th best winning percentage in franchise history).
Doug Moe
Second to Pop in all-time coaching wins for the Spurs with 177. Had a winning percentage of 56.7%. Coached the Spurs in their first season in the NBA. George Gervin won three of his four scoring les under Moe. The Spurs never averaged less than 114.5 points with Moe as coach and his exciting style of coaching helped keep fan interest in those early days. Was the coach during the '79 playoffs when the Spurs were up 3-1 in the ECF and were only one win away from an NBA Finals meeting against the Seattle Supersonics . . .
Mike Mitc
Played for the Spurs for parts of seven seasons. Averaged 20+ points four of those seasons. Averaged 20.1 points and 5.5 rebounds per game while with the Spurs. Fifth All-Time in franchise history in points scored behind Gervin, Robinson, Duncan and Silas. Fourth All-Time in franchise history if field goals made behind Gervin, Robinson and Duncan.
Peter Holt
The owner during all four championship runs. Helped get the SBC Center built which allowed the Spurs to stay in San Antonio. Has been a hands-off owner and let the basketball people handle basketball business. Has paid luxury tax money at various times. Helped pass the current CBA which is very friendly toward small market teams.