Without Brad Delp's soaring vocals, Boston's first album might have been just a bunch of really cool guitar-focused demos by Tom Scholz.

The singer's ability to move from heart-rending tenor to stadium-rattling falsetto, often through the use of stacked overdubs, created a remarkable counterpoint to Scholz's basement tapes. Boston's self-titled album became the second-bestselling debut of all time, and a quick ride to superstardom for a band that initially included only two official members: Scholz and Delp.

In time, others came and went and – after Delp's suicide on March 9, 2007 – Scholz would be considered synonymous with Boston. Still, without Delp, there would have been no band. Scholz had found someone who shared his passion for studio perfection, and someone who could match his guitar pyrotechnics step for step at the mic.

“In my case, I would literally close my eyes while I was overdubbing a part and I would imagine myself being on a stage with thousands of people. I’ve told this story many times, but it’s the way I was able to make it work," Scholz told the Union Leader in 2016. "So, when I was playing, I wasn’t just laying done some tracks or some notes. I was performing, and I was trying to play with the maximum intensity that I could. Brad had the same ability to do that with vocals. ... He could do the same thing, create basically the orchestral vocals in the same way that I could create the orchestra of instruments. It was really the key to making all of the whole recording work, which was the two of us.”

Born in 1951 in Danvers, Mass, Delp grew up as a Beatles fan, and in his last years led a side band focused on the Fab Four's music called Beatlejuice. He began singing with local groups as a kid, eventually forging a friendship with Scholz as the '60s drew to a close. Even then, he battled emotional demons. “I have had bouts of depression and thoughts of suicide since I was a teenager,” Delp wrote in a suicide note.

Their dreams of rock stardom seemed far away then. At one point, Scholz worked at Polaroid while still in school at MIT. In the meantime, he and Delp toiled on the club circuit, while crafting the homemade recordings that would become 1976's Boston.

Watch Brad Delp Perform 'More Than a Feeling' With Boston

That debut sold more than 10 million copies in the U.S. alone. A rushed-out follow up, 1978's Don't Look Back, would be considered a lesser effort, but Boston's sophomore album went an impressive seven-times platinum too.

Through that early rush of success, Delp remained as pivotal as he was humble. "I am just totally lucky to be the guy who was there," he told Classic Rock Revisited in 2003. "When I saw Tom play for the first time, it was just instrumental because the singer who had been in his band had just moved out of town. When I met him, the band was looking for a vocalist. I auditioned and got the gig. I think it is the guy who sings that people sing along with, but he wrote most of the songs."

Within a year, the original lineup had splintered. Scholz continued to speak well of Delp, even as eight years passed between Boston albums.

“The nice thing about Brad,” Scholz said in an '80s interview, “was his incredible ability in the studio. He was a master at controlling his voice — he could do things over and over, changing one note and doing everything else the same. He’s a natural overdubber. He can perfectly match what’s on tape. He can sing harmonies with himself and keep dozens of parts in his mind.”

Boston's songs remained ubiquitous on classic-rock radio, paving the way for their return. In 1986, Third Stage became the band's second No. 1 LP, selling four million copies in the U.S. and spawning their first-ever No. 1 single in "Amanda."

It was almost as if no time had passed ... unless you studied the album credits. Second guitarist Barry Goudreau hadn't been involved in Third Stage at all, while drummer Sib Hashian and bassist Fran Sheehan were there only for a series of very early sessions. Boston were a shadow of their former selves, and soon Delp would depart too. He wouldn't appear on another album for 16 years.

Listen to Brad Delp Perform 'We're Ready' With Boston

Corporate America, released in 2002, became the first Boston album that failed to go at least platinum. That did nothing to dampen Delp's enthusiasm for their reunion. "I have done other projects, and I have nothing against them, as they were fun, but there is only one person who can make a Boston album, and that is Tom," Delp told Classic Rock Revisited. "I think it is as much what he did with the vocals [as a producer] as what I did with singing."

Over the years, Delp's relationship with Scholtz had taken a rocky turn. He worked on several Boston-related projects without the guitarist. That included Goudreau's 1980 self-titled solo album, which also featured Hashian. Delp and Goudreau were also part of Orion the Hunter (along with later-era Boston member Fran Cosmo), and then RTZ in the early '90s.

Each time, Delp eventually returned to Boston, first on Third Stage, then for the tour in support of 1994's Walk On LP, which featured Cosmo on vocals. Delp also sang three new songs for a 1997 Boston compilation before Corporate America arrived. Still, that long history of internal struggles within the band, personal problems and depression seemed to overtake Delp toward the end of his life, and he ultimately killed himself.

Fans were left to chase small scraps of memory. Boston's 2013 album, Life Love and Hopeincluded four songs with leftover vocals by Delp. Goudreau also released a song they'd been working on. Unfortunately, fame didn't provide much solace for the big-voiced and deep-hearted Delp, who concluded another suicide note by writing, "I am a lonely soul."

See Boston Among the Top 100 Albums of the '70s