Even over the past few seasons, with Halladay well-entrenched as one of baseball's premier starting pitchers, he'd chat with Campbell after many of his outings. A relationship that began as pure instruction, back when Halladay was around 12 years old, transformed into a special association as the right-hander obtained more experience through the years.
"You know everything he's going to say, and you know it by heart," said Halladay. "But there was something about hearing it from Bus that made it special. I feel like I got as much as I could from him, and later on, it just became more of a friendship and it was just fun to talk to him."
As Halladay worked his way up Toronto's organizational ladder and eventually into the No. 1 spot in the club's rotation, capturing the 2003 American League Cy Young Award along the way, seeing Campbell became increasingly difficult. This past offseason, Halladay was able to take his family to Colorado to spend some time with Campbell and his wife, Helen.
During the December visit, the older of Halladay's two sons, 7-year-old Braden, was eager to show the aging instructor his pitching delivery. Campbell offered up some bits of advice, reminding Halladay of when his father, also named Roy, took his son to see the pitching coach years ago.
"Braden went through his mechanics, and Bus gave him little pointers," Halladay said. "That was cool. We took some pictures and I got a ball signed from him. It's been so hard to get out there and visit with people, so to be able to have the timing where I got to see him before he passed, I'm just fortunate the way it worked out. I'm glad we made it."
When Halladay was about 10 years old, his dad took him to see Campbell, who was speaking at a local function near Denver. Campbell told Halladay's father to bring the boy back when he was a few years older and he'd agree to begin working with him then. So that's what Halladay's father did, and a brilliant career was officially set in motion.
Halladay credits his father for his worth ethic, but he is quick to praise Campbell for the mechanics he uses to baffle hitters to this day. Campbell coached Halladay through his years at Arvada West High School in Colorado and continued to work with the pitcher after he was selected with the 17th overall pick by Toronto in the 1995 First-Year Player Draft.
"Honestly, I think he was the biggest help for my career," said Halladay, who reached 100 career victories faster than any pitcher in Blue Jays history last year. "A couple of times a week, he'd go over video with me. He'd meet me pretty much anywhere. We'd throw and he got me ready for every Spring Training when I started playing.
"He put in so much time and not only with me. There were hundreds of kids all over Colorado that he was helping, and he never took a dime. He never would accept anything. He really believed he was put here to help kids. That's why he did it."
That selfless approach by Campbell is an attribute that Halladay tries to apply to his own life. Halladay is a quiet leader inside Toronto's clubhouse -- a player who'd rather lead by example than with words. Halladay is always willing to talk, though, especially to younger players who show interest in learning from his experience.
"One thing about Bus is he never seemed to approach anybody and offer his help," Halladay said. "He waited until they came to him, and that's when he was at his best. I think I've kind of taken that approach. I love helping the young guys, but I don't want to force things on them.
"If they have questions or they want to talk, then I'm always more than willing to share with them anything I've got. That's kind of the approach I've taken and there's guys who definitely want to learn."
Last season, Halladay went 16-7 with a 3.71 ERA and he led the Majors with seven complete games. It was his second 16-win season in a row and the fourth time in the past six years that he'd won at least that many games.
This year, he's set to start on Opening Day for the Blue Jays for the sixth straight season. Halladay will lead a rotation that also includes A.J. Burnett, Dustin McGowan and Shaun Marcum, forming a quartet that has the potential to be one of the best groups in baseball.
"Every year, he proves why he's the kind of guy he is," Blue Jays general manager J.P. Ricciardi said. "He's got time for everybody. You hate to say this, but you almost take Roy for granted because he's so consistent. You know he's going to be the first guy in the training room every day to get his work done. You know he's at the park before everyone."
Those are character traits that Halladay learned from his father, but also from Campbell, who also worked with pitchers Jamie Moyer, Brad Lidge and Hall of Famer Goose Gossage, among others. After Halladay signed with the Jays in 1995, he used money from his bonus to buy a grandfather clock for the coach, because the pitcher viewed Campbell as a grandpa of sorts.
"As I go on," Halladay said, "if I get a chance to help people and be able to share knowledge the way he did, that's what I'm going to take from him. I almost owe that to other kids and other people, being able to share that. I was fortunate enough to have somebody do that for me."
Campbell may be gone, but Halladay will always hear his voice.