Steve Miller was convinced his career was about to end.

It was 1973, and the then 30-year-old, who'd been gigging professionally since his early teens, had already released a half-dozen albums and had a smattering of successes with "Living In The U.S.A." and "Space Cowboy." But the record label wanted monster hits – or else.

"This was like a last chance kind of moment for me. I was on my own, I wasn't trying to do anything like anyone else and didn't care about hit singles but just wanted a good album," Miller tells USA TODAY of his breakthrough album "The Joker," a 50-year-old gem that gets a massive box-set treatment called "J50: The Evolution of 'The Joker.'"

"J50" includes three albums plus a 7-inch disc as well as a photo-filled booklet with essays by Miller and rock biographer Anthony DeCurtis. (The physical box set is $179.98, available on Amazon as well as the Steve Miller and Universal Music Group online music stores. A digital version is also available on iTunes.)

"I wish I could say I knew 'The Joker' would be a hit single," Miller says with a laugh as he prepares for a gig in Seattle. "But I had no idea."

In October 1973, "The Joker," replete with a quizzical cover featuring Miller in a kabuki-style mask (the result of him being shy about photos), landed in stores just as Miller and his new band – Gerald Johnson on bass, Dick Thompson on organ and John King on drums – hit the road.

Initially, Miller slipped "The Joker" into his opening acoustic set, still unconvinced of its power. But the rollicking album version was soon in demand from fans, who found themselves hooked by its irrepressible opening lyrics: "Some people call me the space cowboy, yeah/Some call me the gangster of love/Some people call me Maurice/'Cause I speak of the pompatus of love."

"Pretty soon it seemed you couldn't turn on the radio without hearing it," says Miller, still sounding amazed at the turnaround in his fortunes. "They didn't call things viral then, but that's what happened."

Why was 'The Joker' such a hit? It had five hooks, says Steve Miller

What was it about "The Joker" that clicked? In his liner notes, Miller explains: “To make a hit record, I thought it was best to have five hooks. Not one, not two, not three, not four, but five, if you really wanted to deliver a hit. ... Some people call me the Space Cowboy.’ What the hell was that? Then it continues and it gets your attention again: the slide guitar, the chorus, the harmony, the wolf whistle. It all adds up.”

The album of course is far more than just "The Joker." Other tunes on Miller's lynch-pin recording include the raucous "Sugar Babe" opener, the syncopated "Shu Ba Da Du Ma Ma Ma Ma" and a live version of "Evil." But the real treasure trove of "J50" is in the eight unreleased songs and 27 private tracks that give fans insights into how an artist comes up with ideas, workshops them, and ultimately commits them to posterity.

By way of example, Miller explains (in one of a variety of narrated voice-overs recorded for "J50") that a song called "Lidi" was tinkered with repeatedly on Miller's four-track tape recorder to the point where it wound up contributing the chords to the chorus of "The Joker."

Miller attributes the archival motherlode to the exhaustive work done by his wife, Janice, who "went through 600 hours of audio and video I'd saved and got it down to 20 hours for me to look at. I'm amazed at the things she found, like the home movies of me. I was a kid."

Miller is no longer a kid; he's pushing 80 and still on the road, much like his mentor and godfather Les Paul. He wouldn't have it any other way, especially considering he felt the sun might be setting on his career a half-century ago. And then "The Joker" landed.

"The box set is a sweet look back at a period of timed when I was really stressed out," he says. "I thought it was over. But 50 years later, well, it all worked out."