The show's co-creator, star and executive producer paid tribute to the late director - who was found dead, alongside his wife Michele Singer Reiner, at his home on Sunday - and recalled how the When Harry Met Sally filmmaker agreed a four-episode season one pick-up with NBC after the comedy series tested poorly with the 1989 pilot episode.
Seinfeld wrote on Instagram: "Next to Larry David and George Shapiro, Rob Reiner had the biggest influence on my career.
"Our show would have never happened without him. He saw something no one else could. When nobody at the network liked the early episodes, he saved us from cancellation.
Seinfeld admitted he was "naive at the time" to appreciate the impact having the support of Reiner - who co-founded Castle Rock Entertainment, which produced Seinfeld - was for the show.
He said: "That I was working with Carl Reiner's son, who happened to be one of the kindest people in show business, seemed unreal.Â
"I was naive at the time to how much his passion for us meant."
The 71-year-old comic went on to pay tribute to Reiner's wife and described the couple's deaths as "impossibly sad".
He wrote: "Rob and Michele married right as our show was starting and they became an imprint for me of how it's supposed to work, each one broadening the other.
"Their death, together, is impossibly sad."
The couple's son Nick Reiner has been arrested over the couple's murders and is being held without bail.
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