SAN FRANCISCO — About a month after Donald J. Trump was elected president in 2016, Larry Page, the Google co-founder, was summoned along with other prominent tech executives to a meeting at Trump Tower.

It was a rare public appearance for Mr. Page. He sported a tan suit and shifted in his seat as he introduced himself and noted (incorrectly) that his company was probably the youngest in the room. “Really glad to be here,” said Mr. Page, who did not look glad to be there.

By the time he was again summoned in 2018 — this time to testify to Congress on tech’s various problems — Mr. Page had all but abandoned the roles typically associated with leading one of the world’s richest and most powerful companies. He didn’t show, and senators placed an empty chair and his placard alongside the other speakers.

On Tuesday, Mr. Page and Sergey Brin, his Google co-founder, said they were stepping down from day-to-day executive roles at Alphabet, Google’s parent company. While the move seemed sudden, it was the culmination of a yearslong separation between two of Silicon Valley’s most prominent founders and the company they began 21 years ago.