Bill Cowher coached the Pittsburgh Steelers from 1992 to 2006. In that time frame, he had six different offensive coordinators. The Buffalo Bills have already employed three of those six coordinators (two as head coaches), and another may very well be on the way.
Ken Whisenhunt, who is emerging as a leading candidate to become the Bills' next head coach, was Cowher's offensive coordinator from 2004 to 2006 before he left - following Cowher's resignation and the subsequent hiring of Mike Tomlin - to become head coach in Arizona. He held that job for six years before getting fired on Monday.
Whisenhunt replaced one Mike Mularkey as the Steelers' offensive play caller in 2004 when, after the 2003 season, Mularkey left the organization to become the head coach of the Bills. Mularkey was drawn to the job by the presence of President and GM Tom Donahoe, who had landed in Buffalo after leaving the Steelers organization - for which he worked nine years as the director of football operations - following a lost power struggle with Cowher.
Mularkey was Cowher's choice to replace Kevin Gilbride as his offensive coordinator, who spent two seasons in that job in 1999 and 2000. Gilbride worked for the Bills for two years, as well; he was Gregg Williams' offensive coordinator in 2002 and 2003, before Williams was fired and replaced by Mularkey.
Gilbride's immediate predecessor was Ray Sherman, who spent but one year on the job in between stints with Minnesota. Sherman was hired to replace Chan Gailey, who called plays under Cowher in 1996 and 1997 before leaving to become head coach in Dallas. (Gailey replaced Ron Erhardt as offensive coordinator, who was Cowher's first play caller and worked there for four years.)
A pipeline between the Bills and Steelers has existed for years. Donahoe helped start it when he ran the Bills, which led to Mularkey's hiring as head coach. It continued when the team pursued Cowher as head coach in 2010, who recommended Gailey for the job while turning it down. A month after Gailey was hired, the team brought in Doug Whaley - who spent a decade as the Steelers' pro scouting coordinator, working alongside Cowher for seven years - as the Assistant GM and purported "GM in waiting."
Now, the team is not only interested in Whisenhunt, but two more former Steelers assistants that worked under Cowher: Ray Horton (defensive backs, 2004-2006 with Cowher, 2004-2010 in total) and Russ Grimm (offensive line, 2001-2006). Embrace the Pittsburgh coaching tree, folks, because the Bills have been into it for years.