Since 2011, Rieker has been the Director of Umpire Development for Major League Baseball. He coordinates a wide variety of training and educational initiatives and works closely with Major League umpires. He joined MLB in 2002 as an umpire supervisor after spending ten seasons as a Major League umpire. Since 2006, Rieker has been responsible for administering Major League Baseball Umpire Camps which have trained over 6,000 umpires during the last ten years. He produced a “Virtual Umpire Camp” CD-ROM which illustrates the proper procedures for umpires. Rieker was a National League umpire from 1992 to 1999. In 2000 and 2001, he worked in both the National and American Leagues. He umpired 1,001 Major League games during his ten-year career. He umpired in two division series (1999 and 2000) and the 1998 All-Star Game. He was behind the plate when Mark McGwire hit record-breaking home runs 69 and 70 on September 27, 1998. Rieker was a minor league umpire for ten seasons from 1983 to 1992, working in the Midwest League, the Eastern League, the American Association, and the Dominican Winter League. He finished first in his class at the Harry Wendelstedt Umpire School. Rieker was an instructor at the school for 16 years. He grew up in St. Louis and attended St. Mary’s High School and the University of Missouri at St. Louis. He first started umpiring in the Khoury League when he was 11 years old. Rieker was a member of the Greater St. Louis Association of Umpires, working high school, college, and American Legion games.