In the British rock scene at the end of the 1960s, the Stones were the bad boys; Black Sabbath was devilish; Led Zeppelin was writing the best songs and Pink Floyd was doing psychedelic stuff. But Deep Purple was "the loudest pop group in the world." Employing a Hammond organ, hard guitar riffs and Ian Gillan's distinctive vocals, Deep Purple were the forefathers of hard rock and heavy metal.

In April 1968, Rod Evans, Jon Lord, Richie Blackmore, Nicky Simper and Ian Paice form their new band, record an album and make a hit with their single "Hush." Two albums later, the group makes changes: a different record label and different band members. Ian Gillan replaces Evans on vocals; Roger Glover follows Simper on bass guitar. The legendary "Mark II" team is up and running.

This cast of band members gives a landmark performance: a concert at Royal Albert Hall, accompanied by the Royal Philharmonic Orchestra. A rock band had never played there before. Deep Purple could do it because they had created a masterful combination of rock and classical music - largely due to the classically trained keyboardist Jon Lord. The "Concerto" became Deep Purple's first live album.

The "Concerto" was lovely and all. But just to ensure people didn't forget what kind of music they really were doing, Deep Purple took a harder line. On the album "In Rock," songs like "Speed King" and "Child in Time" showed people what they were all about: total hard rock with classical elements, along with Gillan's explosive vocals. It was a global breakthrough and garnered gold numerous times.

With the award-winning double LP "Live in Japan," Deep Purple reaches its "Mark II" zenith in 1973. After years of hard work, the band implodes - Glover and Gillan leave. David Coverdale takes up the microphone. But the "Mark III" line-up doesn't last even two years. Blackmore leaves because he can't stand Coverdale. His replacement, however, cannot fill the gap, and the band breaks up in 1976.

The legendary "Mark II" line-up is together once again - a record label allegedly offered each musician a pretty penny. The boys get right down to business: The album "Perfect Strangers" serves up the old Purple sound, but with fresh elements. Their fans are grateful, and the album goes Top Ten everywhere. The band tours, and everything is going well - until Gillan and Blackmore lock horns again.

Ian Gillan leaves the band again after four years. A new vocalist steps in, but the band is losing steam. All the personnel changes rattle fans as well. The 1990s album "Slaves & Masters" does not garner much praise; the new singer has to leave. Much to Blackmore's chagrin, the band again tries to win Gillan back. And he does come back one last time.

The band patches things up and manages to make another good album together. But between two tours, Blackmore exits for the last time. Joe Satriani steps in for him and plays the Japan tour. And the weird back-and-forth of the band line-up continues. The band continues to produce albums and tours - up until today.

Of course, the band also has to perform at the biggest heavy metal festival in the world - in Wacken, Germany. In 2013, Deep Purple opens its gig in front of 75,000 people with "Highway Star." Ian Gillan appears a little feeble. Still, the live album "From the Setting Sun…" is released, and simultaneously "…to the Rising Sun" - with a live recording from Japan.

The Montreux Jazz Festival in Switzerland is famous for expanding the boundaries of jazz. That's why Deep Purple are welcome guests at the festival. They were there in 1971, when a fire broke out during Frank Zappa's concert. Jon Lord followed that up by writing Deep Purple's biggest hit: "Smoke on the Water." It vies with "Satisfaction" for having the most famous guitar riff of all time.

The old Deep Purple champs Ian Gillan, Ian Paice and Roger Glover still play everywhere these days. Don Airey took up Jon Lord's place at the keyboard, after he passed away in 2012. Steve Morse plays guitar. And now in their 60s and 70s, they're still rockin'.