For a guy who comes across as soft-spoken and genial, Peter Lassally hardly projects the aura of a Hollywood power-broker. Yet it’s hard to find many major developments in latenight television over the last 40-plus years that haven’t involved him, from relocating Johnny Carson to Burbank to steering David Letterman to CBS to, if Lassally had had his way, establishing Jon Stewart as Letterman’s heir, which potentially could have rewritten the genre’s next chapter.

After a career that dates back to Arthur Godfrey, Lassally, at 82, decided to retire. Coupled with Letterman’s departure this spring, it feels like the end of an era.

The man who earned the nickname the Host Whisperer claims to possess only one demonstrable skill — an ability to identify talent. That eye helped launch countless comics during his “The Tonight Show” tenure, back when an “OK” signal from Carson could propel a standup performer from small clubs to arena tours.

Lassally worked for Carson until the end, then joined Letterman’s Worldwide Pants. He played a pivotal role in Letterman’s decision to leave NBC, and championed Craig Ferguson’s move into the 12:30 slot. When the company had a holding deal with Stewart in the mid-1990s, Lassally pushed for him to replace Tom Snyder behind Letterman. Overruled, the gig went to Craig Kilborn, and Stewart left to supplant Kilborn at “The Daily Show.”

In hindsight, it’s mind-boggling to think about how many careers that one decision influenced, among them that of Letterman’s eventual successor, Stephen Colbert.

Perhaps fittingly, Lassally spent the last few months overseeing guest hosts in advance of James Corden’s March 23 “Late Late Show” premiere. Those shows represented something of a throwback to the days before Letterman and Jay Leno became latenight kingpins, and began airing reruns during their time off instead of relying on guest hosts — a byproduct of the insecurity engendered by the Carson succession battle.

Lassally fully embraced Letterman in that storied baton pass, and stayed friendly with Carson after his retirement. He even served as a conduit for Carson, who, missing his monologue, quietly fed jokes to Letterman over the years.

“He changed completely after he left,” Lassally said of Carson. “He was more relaxed and outgoing.”

Asked to assess the two hosts’ strengths — each of whom endured a staggering 30 years behind the desk — Lassally said, “Carson was uniquely suited to that job, because he could reach everybody. Letterman had an edgier side.”

Despite hanging up his spurs, Lassally’s influence will continue, including the many producing proteges he has cultivated.

CBS Entertainment chairman Nina Tassler referred to him as “the strong, silent type,” with an unerring ability to “diagnose problems with surgical precision” and a nurturing attitude that elicited the best from the big personalities with whom he’s dealt, as well as with the show’s staffs.

“He’s kind of ego-less,” Tassler noted. “There’s a comfort he derives from not wanting or needing to be in the spotlight.”

Assessing the current turnover in latenight, Lassally is skeptical that Comedy Central can find a replacement capable of filling Stewart’s shoes. “Whatever they’re going to do, I don’t see it working,” he said.

As for pet peeves, Lassally wishes guests would be more conversational and interactive with hosts, instead of playing to the audience. “The people who teach actors how to be talkshow guests, they do it all wrong,” he said.

CBS threw Lassally a party to commemorate his retirement, but he was uncomfortable when a few speakers used the term “legend.” All he aspires to in terms of a legacy, he said, is being remembered as “a decent fellow.”

For a producer who spent years watching someone step from behind a curtain, that’s certainly a nice note on which to close it.