That tour not only led to Shepherd's first concert album, Live! In Chicago, it also produced something far more special.
"Getting to know Hubert, he's become like a father to me, you know," Shepherd said. "That in itself is the most precious thing that I've taken away from the whole experience, is the personal relationship that I have with Hubert now."
The 79-year-old Sumlin also felt that special bond, one that reminds him of his days as a young guitarist with The Wolf. Sumlin remembers being terrified of the imposing Chester Burnett when he first met the fiery 300-pound singer, but he also remembers being determined to learn from the best.
"He wasn't going to stop me," Sumlin said. "I just looked at him, man. He said, 'Boy, I know you don't like me, but I think you just like what I'm doing.' I said, 'Yes, sir.' And he sat down, man, and showed me things Charlie Patton had shown him."
Wolf hired the then-18-year-old for his band, and Sumlin spent the next 25 years refining a style that became a siren's call to guitarists for the last 50 years.
When the 33-year-old Shepherd decided he wanted to do a live album, he didn't want to offer fans reheated hits. He invited Sumlin, along with others who have influenced him along his journey to becoming one of the blues' finest young players - Willie "Big Eyes" Smith, Bryan Lee and Buddy Flett.
He let each help pick which of their songs the band would play on the record and the resulting concert has a varied, celebratory feel. It spent four straight weeks at No. 1 on the Billboard blues chart when released earlier this fall.
Sumlin's unique finger-picking style is on display on the Wolf songs "How Many More Years" and "Rocking Daddy," and his own "Feed Me." His airy, bouncing guitar lines can alternately dance with gleeful abandon and spread a feeling of dread and menace.
"His style is pretty cool, with the way he plays without a pick and everything," Shepherd said. "Watching him, he's got a real interesting vibrato. To see everything up close and firsthand is definitely a learning experience for me. He can hit his stride still. In his prime nobody could touch him. He had that signature sound."
Despite a heart attack and having a lung removed due to cancer in 2002, Sumlin remains active and has a robust schedule for a man his age. He's still the nattiest dresser on stage in a suit and hat, but he will accept the offer of a chair during sets.
"You know what? I love what I'm doing, man," Sumlin said. "I've done worked sick so many times. When they took the lung away from me I was back to work about two or three weeks after that. I couldn't stand up on the bandstand. They let me sit down. I appreciate it. I can work sick, it doesn't matter. As long as I ain't dead."