By the 1970s, the new Aztecs had become one of the most popular hard rock bands in the country with appearances at the Sunbury Pop Festival and hit songs such as "Most People I Know (Think That I'm Crazy)", before disbanding in 1973.
Over the next twelve months the band reigned supreme as the most popular 'beat' group in Australia, scoring further hits with the songs "Mashed Potato", "Sick and Tired" and "Somewhere Over the Rainbow", until they were eclipsed by the emergence of The Easybeats in 1965.
During 1965 the original Aztecs quit after a financial dispute, so Thorpe put together a new five-piece version consisting of drummer Johnny Dick, pianist Jimmy Taylor, guitarists Colin Risbey and Mike Downes and NZ-born bassist Teddy Toi.
Thorpe went solo in 1967 and for a brief time hosted his own TV show, It's All Happening, but personal problems and a widely publicised bankruptcy brought this phase of his career to an end in 1968.
In 1969, Thorpe decided to try England, after being offered a recording deal by the Australian-born, London-based impresario Robert Stigwood, who had risen to become manager of The Bee Gees and Cream.
While rehearsing a backing band in Melbourne that would form the basis for a new Aztecs, the guitarist unexpectedly dropped out, leaving Thorpe to assume lead guitar role at short notice.
Thorpe had also drastically changed his appearance—he grew a beard, often wore his now shoulder-length hair braided in a pigtail, and he had long since traded the tailored suits for jeans and T-shirts.
Needless to say this did not endear him to people who came to the shows expecting the 'old' Billy Thorpe of the "Poison Ivy" era, and this led to sometimes violent confrontations with disgruntled fans and promoters.
According to Thorpe, the band (which at this time comprising himself, Murphy, pianist Warren Morgan, Lobby Loyde and bassist Paul Wheeler), were all high on LSD and jammed continuously while engineer Ernie Rose just let the tapes roll.
The result heralded the fully-fledged arrival of the new Aztecs and live shows at Melbourne venues consolidated the band's reputation and drew enthusiastic responses.
Now a four-piece following the departure of Loyde, the Aztecs (Thorpe, Morgan and Wheeler, with new drummer Gil "Rathead" Matthews) headlined a major concert at the Melbourne Town Hall before a capacity crowd of 5000.
In early 1972 the Aztecs released what became their biggest hit, and Thorpe's signature tune – "Most People I Know (Think That I'm Crazy)", a song now widely regarded as one of the classics of Australian rock.
Thorpe himself claimed this as a pivotal moment in the development of Australian music, thanks to the promoters' decision to feature an all-Australian line-up, rather than relying on imported stars.
The Aztecs shared billing with such other prominent acts as Spectrum/Murtceps, The La De Da's, Max Merritt & the Meteors, SCRA, Pirana, Greg Quill's Country Radio and many others.
He released several more solo albums in Australia before re-locating to the United States, where he embarked on a series of business ventures, including a successful toy company with his old bandmate Tony Barber.