Walter Becker of Steely Dan performs during the Jazz and Heritage Festival in New Orleans on May 6, 2007. Becker, the guitarist, bassist and co-founder of the rock group Steely Dan, died Sept. 3 at age 67. (Dave Martin/AP)

Steely Dan's Walter Becker wasn't a flashy guitarist or great singer. His genius came in his partnership with Donald Fagen, which began at Bard College in the late 1960s, stretched over seven albums from 1972 to 1980 and a pair of surprisingly strong late-period records after he and Fagen regrouped in 1993.

And with Becker's death on Sunday, at 67, we also mourn the end of that partnership, what he and Fagen called a concept more than a rock group: Steely Dan.

Over an eight-year stretch, Steely Dan produced a catalogue like no other. They were as subversive as they were popular, and with songs such as "Peg," "Rikki Don't Lose That Number" and "Hey Nineteen," they were very popular.

Like most partnerships, it's hard to pin down the division of labor. Becker, in an excellent 2008 interview, danced around the question. "So whatever needs to be done, sometimes I've got something to start with, sometimes Donald's got something to start with," he said. "Sometimes we really work very closely, collaboratively on every little silly millimeter on the writing of the song and certainly of the records, and sometimes less so."

The body of work doesn't lie. Fagen, the group's keyboardist and singer, and Becker, the bassist at first and later rhythm guitarist, were capable and always interesting as solo artists. But together they were special, with a gift for misdirection and an impeccable taste in music. Who else would cover a 1920s Duke Ellington tune, "East St. Louis Toodle-Oo," at a time when Chicago, John Denver and Bad Company ruled the charts?

They started Steely Dan as a regular rock group, recording and touring throughout the early 1970s. Then Fagen and Becker decided they wanted off the road and, after a show in the summer of 1974, stopped touring. In the studio, they crafted their records by recruiting some of the best players of the day, including guitarist Larry Carlton, saxophonist Wayne Shorter and vibraphonist Victor Feldman. Steely Dan's eventual demise, after 1980s "Gaucho," came after conflicts with their record company and also with the mother of Becker's ex-girlfriend. She died of an overdose, and Becker, addicted to drugs at the time, was sued for wrongful death, a case he eventually won. He eventually stopped using.

What made Steely Dan special — and it's not an overused word in this case — came from the great paradox of making music often as smooth as the Doobie Brothers but as dark, twisted and unreliable as the work of their literary hero, Vladi­mir Nabokov. Speaking of the Doobies, for a time singer Michael McDonald bounced between both bands.

In fact, almost everything about Steely Dan was a paradox. They were album-based yet scored with singles throughout the 1970s. They were a band that quit the road at their commercial peak and yet returned to the sheds in 1993, 13 years after what had been their final studio record. (Maybe only Brian Wilson's emergence as a road hog was more surprising.) Fagen admitted at times that they played gigs out of necessity, as royalties dwindled. After all, Steely Dan wasn't a band about to score millions off a jam-band cover or a movie soundtrack. The calypso rhythms of "Everyone's Gone to the Movies" don't work quite as well in "Happy Feet" once you realize it's a song about a dude who shows the neighborhood kids dirty movies.

There was something strange about Steely Dan returning to the road. Fagen said as much as he lamented that the band's core concert audience didn't take well to their playing a chunk of songs from their excellent 2000 reunion record, "Two Against Nature." (He also slammed me for what he perceived as an unfair attack when Steely Dan scored a slot at Coachella.)

The cause of Becker's death was not released. His decline was noticed. He had missed the group's high-profile dates at the Classic West and Classic East festivals this summer. In May, fans worried about his bloated appearance at a Steely Dan show. What Fagen made clear in his brief statement for his friend is that the concept, which they developed together over decades, will not end with his death.

"I intend to keep the music we created together alive as long as I can with the Steely Dan band," he wrote.