Castro, 56, will be serving under his seventh different full-time or interim manager in 2009, his 18th season on the Major League coaching staff and his 35th season in some capacity with the Brewers as a player, scout or coach. He will replace Mike Maddux, who had an offer from the Brewers to return for a seventh season as pitching coach but instead took a richer offer from the Texas Rangers.
Castro was the only candidate interviewed for the Brewers' opening.
"I think he's earned the opportunity do this," Brewers general manager Doug Melvin said. "In the end, the familiarity he has with our team and the rest of our league came into play. I didn't necessarily want someone who was going to come in who was going to change our pitchers' mechanics.
"Ken and I talked at length about a number of other people. There weren't really candidates out there that we both really agreed upon. The other thing is that if we would have gone out and hired a Triple-A coach or a roving coach, I don't think that would have been fair to Billy and I also don't think they would have had the experience that Billy has."
Castro had already signed a contract to return as bullpen coach. Now he will work with Melvin on a new deal, probably for one season. The Brewers are also bringing back first-base coach Ed Sedar and Dale Sveum, who finished last season as the interim manager but will move into the role of hitting coach.
Macha went outside the organization for third-base coach Brad Fischer, a colleague from when both were in Oakland. The Brewers still need to hire a bench coach and now a new bullpen coach to replace Castro.
Castro traveled to Pittsburgh on Wednesday for a 2 1/2-hour lunch meeting with Macha. Two days later, he had the job.
"It's especially nice to get it here in Milwaukee, the organization that signed me," Castro said. "I came through the ranks of the Minor Leagues and got to the big leagues for seven years, then left for three years, came back and never left. Now I'm the pitching coach, so I'm really pleased with that."
Bolstered by the midseason addition of CC Sabathia, the Brewers finished the year ranked second in the National League with a 3.85 staff ERA.
Top starters Sabathia and Ben Sheets are both free agents, and while the Brewers have extended an initial offer to Sabathia, it is very possible that both will depart. That would leave the Brewers with a rotation of Yovani Gallardo, Manny Parra, Dave Bush, Jeff Suppan and Seth McClung, barring other moves by Melvin.
"I like all of our guys," Castro said. "They're all good pitchers, and they are all different. That's what I have to understand, that you can't clone everybody. Everybody has different things that they can do, and there is a reason they got to this level. My job is to help them stay consistent. I'm not going to come here and reinvent the wheel."
Does he intend to institute any new staff philosophies?
"My main philosophy is that every pitcher is different," Castro said. "If you remember that, that there are different things that every guy is capable of doing, you'll be OK."