In pop music, what's just as important as who is behind the microphone is who is behind the scenes - the ones crafting the lyrics, the vocal direction, and the overall song itself. Most times, the artist is the one responsible for all of that, but other times, there are outside writers bringing the tracks to life, and they always deserve recognition, too. For mastermind songwriter and producer Max Martin, he's been getting his hands dirty in the music scene for almost 20 years, and he just got even more legendary: Martin notched his 18th number one single with Taylor Swift's 'Shake It Off.'

Max Martin Dr LukeMax Martin with Katy Perry and fellow producer Dr. Luke

Martin, whose real name is Karl Sandberg, entered the world of being on top back in 1999: his first ever number one single came in the form of Britney Spears' '...Baby One More Time,' and the second came in the form of 'N Sync's 'It's Gonna Be Me.' Oddly enough, Martin never had another number one until 2008 - and that's when the takeover began. After linking up with the likes of Kelly Clarkson and Katy Perry, Martin's singles began spreading like wildfire the second they hit the Internet. 'Shake It Off,' Martin's newest addition to his number one collection and first single off Swift's 1989 album, is record breaking. He now currently stands behind The Beatles' Paul McCartney and John Lennon for the lone spot at number three - a position he previously shared with Mariah Carey. McCartney and Lennon's numbers come in at 32 and 26 number ones, respectively, so Martin has a bit of a way to go to catch up - but he's definitely going to do it.

More: Watch the music video for Taylor Swift's 'Shake It Off'

On Swift's 1989, he collaborated on a few more songs that are bound to become singles, and he came dangerously close to a few other number ones this year, too. Jessie J's 'Bang Bang' debuted at number six, while Ariana Grande's 'Problem' and 'Break Free' peaked at number two and six, respectively, so Martin could have easily gotten a few other chart toppers as well. While Martin is undoubtedly going to reign supreme on the Billboard rankings for the rest of this year and beyond, you'd be surprised by how many of his songs actually don't get any attention at all. Naturally, he's written and produced an endless amount of tracks in his career, and some just never bothered to become singles - but that doesn't mean they weren't any good. Here are some of the best Max Martin songs that never got the single treatment.

MKTO - 'Forever Until Tomorrow' (2014)
MKTO is quickly becoming dangerously hot in the industry. Led by Malcolm Kelley and Tony Oller, the pop duo first found success in the U.S. with their lead single, 'Classic,' which reached as high as number 14 on Billboard. The band released their self-titled record back in April, and they're currently pushing their next single, 'American Dream.' A record filled with pop hooks galore, Max Martin offers his talents on one of the songs, 'Forever Until Tomorrow,' and it's one of the catchiest songs on the album. For some reason, it hasn't become a single yet, but it's still possible that it could see a radio push sometime in the future.

Next page: Some other great Martin tracks that were never singles