As coach Thomas Lynn Trebelhorn (born January 27, 1948) is an American former manager in Major League Baseball for the Milwaukee Brewers (1986–91) and Chicago Cubs (1994).

Trebelhorn was married since 2000 to former Summerfest director and Milwaukee mainstay Bo Black, until her death on July 24, 2020.

[2][3] He spent five years as a minor league catcher and infielder for the Islanders (and by extension their affiliates the Angels and, later, San Diego Padres) and Oakland Athletics organizations.

In 1975 and 1976, he managed the Boise A's in the Oakland Athletics' Minor League Organization, and it was during this stint (1976) that he was instrumental in teaching future Hall of Famer Rickey Henderson the intricacies of base stealing, based on remarks made by Henderson at his induction ceremony to the 'Hall' on July 27, 2009.

He was a finalist for the San Francisco Giants managerial job in the winter of that year, being one of the final five candidates interviewed, but Dusty Baker was chosen for the position.

[9] The strike that occurred in August of that year stopped the team from doing worse than their record of 49–64 (.434), and he was fired on October 17 by new general manager Ed Lynch.

Following this, he was hired to be the minor league coordinator of instruction for the Baltimore Orioles, his first front office position.

Midway through the 2005 season, he was transferred to the position of bench coach, taking over the role from Sam Perlozzo, who was named interim manager.