From a Jay Jaffe piece for SI back in 2014:
Earlier this week, John Lowe, a writer for the
Detroit Free Press for the past 29 years — and an extremely well-respected one at that —
announced his retirement. If you don't know Lowe by name, you almost certainly know at least one facet of his legacy, for he invented a statistic: the quality start.
The year was 1985, and Lowe was writing for the
Philadelphia Inquirer (he moved along to Detroit the next year). Noting the decline of the complete game and the evolving philosophy of managers with regards to their expectations for their starting pitchers, he strove to find a descriptive stat that recognized this change.
As he told Murray Chass in 2011:
"I got the idea in 1983 and '84," Lowe said. "I was hearing managers saying they were looking for six innings from their pitchers. I heard Whitey Herzog say 'all I want from my pitchers is six good innings.'"
That's where six innings came from. And the runs? "Six and two is too stingy, six and four is too much. I wasn't going to get into a more than or less than. This was new and had to be understandable."
Why the need for a new statistic? "I didn’t like ERA as a definitive stat," Lowe said. "One bad start could wreck your ERA. But I never said don't look at wins and losses."
https://www.si.com/mlb/2014/10/23/quality-start-john-lowe-statistics