So, when the Dodgers began due diligence before launching their record-breaking $147 million pursuit of the right-hander, they didn't look far for inside information.
There were hurdles that needed to be cleared for the Dodgers' comfort level, what with Greinke's history of social anxiety disorder and the reputation of having a sometimes prickly personality. So they asked the bench coach what he learned when he was manager.
You can probably tell by the outcome of the signing where Hillman came down on the question of Greinke's value as a pitcher and a teammate.
"I am extremely excited about him being part of the rotation," said Hillman. "He loves to compete. He had his best stuff against the best offenses, that would really put him on his 'A' game, especially that Cy Young year."
A former coach said Greinke is "different, in a good way." A former teammate called him "Captain Weirdo." Hillman knows why Greinke elicits such unusual reactions. But he said Greinke is not hard to manage.
"He can be a little standoffish. There are days he doesn't speak," said Hillman. "But he's a good teammate, especially with his fellow starting pitchers. My objective was to stay out of his way. I had maybe six or seven conversations with him the whole year. There wasn't really a need for more.
"One thing I told him was I wanted, with his anxiety, to make him comfortable. If he needed something, come to me. I kept the conversations very short. The last thing I wanted in '09 was for him to think I was jumping on the bandwagon."
Hillman said Greinke is serious about pitching and his preparation. He said Greinke was closest to pitching coach Bob McClure.
"They had a great relationship," said Hillman. "Mac told me on multiple occasions that Zack was a sharp, smart guy. He can look at things totally different at times. He doesn't always see things the way others see them. He doesn't mince words. He'll tell you exactly what he thinks. With his teammates, he has a great sense of humor. He keeps to himself, but it's not like he doesn't interact with teammates."
During the process of selecting his team, Greinke came alone to California to meet with Dodgers executives and impressed management by his knowledge of the team and the questions he asked.
Greinke later explained that his decision was based on several factors, among them the chance to win every year with a loaded roster that has already been rebuilt, how that lineup stacked up with other teams making offers (Texas and Anaheim) and a ballpark ideally suited to a fly-ball pitcher.
"I'm not surprised he was driving the process," said Hillman. "That's where Zack's intelligence comes in. He's going to set the course and he's going to drive it. I know he has an agent, but in this situation I'm sure he was the boss."