For Seinfeld, it helped launch his eponymous show to new heights, eventually making him a television icon and zillionaire.
For Hernandez, it introduced him to millions of Americans who didn't know or care about his baseball accomplishments.
It was "The Boyfriend," a two-part "Seinfeld" that premiered in February 1992 and since has been among the series' most beloved episodes, including by Seinfeld himself.
And like many episodes, it is liberally quoted to this day, including in the first paragraph above.
Now, for the first time since that show - and a brief appearance by Hernandez in the finale six years later - the New York pop culture institutions, both 56, are poised to work together again.
Though both often are at Mets games and despite their shared history, Hernandez said it will be the first time he has had any sort of extended conversation with Seinfeld in a "very, very long time."
And it certainly will be the first time they have publicly discussed "The Boyfriend," in which Seinfeld becomes jealous of his friend Elaine's relationship with Hernandez, among other plot developments.
"I'll get to ask him questions regarding his feelings about my performance," Hernandez said.
Does it bother him that some people still primarily know him from the show and still shout references from it - "I can help you move!'' - at him in airports?
"I feel blessed and lucky," he said. "It could have been one of the many ordinary shows that was on, but it was an extraordinary show and an extraordinary episode.''
Hernandez, who last played in 1990, heard the following year from his baseball agent, Scott Boras, that Seinfeld wanted him.
"I said, 'How much [money]?' They said, 'This much.' I said, 'OK,' " Hernandez said.
It was his first opportunity to be an actor. "It was one of the great experiences of my life," he said, "but I can't say I fully enjoyed it, because I was terrified."
As scared as Hernandez was, other actors told him Seinfeld was "shy and nervous" around him. (Seinfeld, who grew up in Massapequa, declined to speak to Newsday for this article.)
One of the plot lines was an allegation by Kramer and Newman that Hernandez had spit on them after a game in 1987. But Seinfeld believed the "second spitter" theory, one eventually proven correct.
It was Hernandez who suggested former teammate Roger McDowell as the spitter. "I said Roger would be perfect, and he won't be camera-shy," Hernandez said.
Curt Gowdy Jr., SNY's executive producer, said Seinfeld will begin in the third inning and work at least three, but that the nature and duration of his role will be determined as the game evolves.
What does Cohen think of the idea? "I think it's fantastic," he said, adding he is an "enormous" fan of the show and has seen "The Boyfriend" perhaps 20 times.
Hernandez said he saw the episode the night it premiered but only a couple of times since. Why? "I can't watch it," he said. "I get too embarrassed."