Three veterans of the West Central Indiana music scene, they had crossed paths several times, but had never collaborated as a unit.
But Jack and Jay, both singers and guitarists, started playing some shows together at Moore's Bar. After a while, they decided to bring on Bill to add another voice and play bass.
What they discovered was harmony gold.
"The three-part harmony was just automatic," Gibson said. "It's one of those that you just know we gotta do something with it."
With that, 15th and Hulman was born. Hailing from Greencastle, Staunton and West Terre Haute, respectively, Jack, Bill and Jay began playing gigs around the western part of the state.
"We became quite popular because of the three-party harmony," Bill said. "We had people ask if we were siblings."
The harmony is more Eagles than Everlys, though. Genetics can't explain it, and neither can the band. They just go with it.
They describe their musical style as "Alan Jackson to Michael Jackson," saying no matter the original style of the song, they make it fit what they do.
"Even if it's not a harmony song, it's harmony when we get done with it," Jack said.
While they are a prolific cover band, each man is also a songwriter. Even the originals cover a wide range of genres, from country to funk and even tropical rock.
Almost by accident, the boys have become well known in the trop rock world, having their song "Pier Night" picked up by internet station "Beach Front Radio."
The music is so popular, in fact, 15th and Hulman was invited to contribute to the cookbook "Cooking with the Trop Rock Stars."
While the band members quip, "We didn't even know we were trop rock stars," there they are on pages 100-103. They share two food recipes, "Hoosier Homemade Waffles" and "Chocolate Gravy," and two drink recipes, a "Hoosiercane" and "A 15th and Hulman Special."
Far from believing they've arrived, though, the band continues to work hard both on the music and the entertainment side of things.
"We've developed a show by entertaining," Jack said. "The harmony was the backbone, but people are gonna be entertained. It's not the same show over and over."
They take this ethic so far, in fact, that shows lack a set list. Between the three men, they know hundreds of songs across several genres. They spend most of a show taking requests, sometimes from the very beginning.
"We purposely put things together for audience participation," Jack said. "There's times that as soon as we start, we're in the middle of the audience.
"Most bands have gigs, we have shows."
At a recent show at the Putnam County Fair, a spectator requested a Carrie Underwood song. While the song was a bit out of any of the men's vocal range, Jay quickly stepped to the mic and said, "We can't do that, but here's a girl song."
They then launched into a strong rendition of Tanya Tucker's "Delta Dawn."
"With all three of us singing, we sing a wider variety of songs," Jay said.
They can also pick each other up. One man may start a song and get to the second verse and realize he doesn't remember it. One of the other two can often take over.
"We've all sang and been in the music business so long, we're like a jukebox," Jack said.
The flexible spirit has opened doors for the band, as they now have frequent gigs in Nashville, Tenn., playing regularly at The Honky Tonk Central, Tootsie's and Rippy's.
Doors have also opened elsewhere, with shows and offers coming from elsewhere in Tennessee, as well as the Carolinas, Missouri and a number of nearby Midwestern states.
In Nashville, the band is also working on its first album, which is about half complete. They've been traveling south each Sunday and Monday to work on the tracks.
Rather than focusing on one genre or approach, they are putting a number of different styles on the album.
"Our idea going in is putting a little bit of everything on it," Jack said. "That way, we're kind of shopping in all directions."
As excited as they are about the album, the trio keeps its focus on the shows, knowing they've made their reputation as entertainers.
"People see with their eyes and see how good a band is when you get somebody live and walking around, entertaining the crowd," Bill said.
15th and Hulman will play The Swizzle Stick in Greencastle at 9 p.m. Friday, Aug. 17. They also have a number of upcoming nearby shows in Brazil, Terre Haute, Danville and Indianapolis.
Learn more about the band at www.15thandhulman.com.