In 2015, he is alleged to have met with Mr Trump and his “fixer”, Michael Cohen, at Trump Tower, where he agreed to “catch and kill” negative stories about the then-presidential candidate.
According to prosecutors, the group hatched a plan to buy exclusive rights to stories without publishing them.
Those years of association were on display at the trial this week, where Mr Pecker, after appearing on the witness stand, gave Mr Trump’s table a smile and a quick “hi”.
Mr Pecker was meant to function as the Trump campaign’s “eyes and ears”, prosecutors claim. If true, that arrangement could prove uniquely damaging to Mr Trump in the days ahead.
Neither man could have foreseen how dramatically their relationship would change since their alleged agreement in 2015.
Marc Liu, the vice president of marketing at AMI, claimed that Mr Pecker attempted to model himself on the New York billionaire over their decades of association.
“He thought of himself like Trump — in the way he ran his businesses, in the way he saw himself, and the way Donald ran his businesses,” he told Politico.
“Everything he did, he did to try to emulate what Trump was doing.”
Another former employee claimed that Mr Trump treated the publishing executive like a “little puppy”, who by contrast saw him as a “king”.
Little emerged from Mr Pecker’s testimony on Monday, in which he confirmed his phone numbers and spoke about the National Enquirer’s editorial process.
