Lochner tutored Kennedy in how properly to pronounce the words “Ich bin ein Berliner” - a phrase that was greeted with thunderous applause by the hundreds of thousands of people who thronged to see Kennedy.
Lochner, who was born in New York but later settled in Germany, recalled that he was sitting in Kennedy's motorcade as it drove through the city when the president asked him to write the phrase.
In a quiet corner before the speech on 26 June, 1963, they rehearsed how he should say it.
Then, at Rudolph Wilde Platz in west Berlin - an enclave controlled by Western powers surrounded by the territory of communist-run East Germany - President Kennedy expressed his solidarity with the city's residents.
"All free men, wherever they may live, are citizens of Berlin," he said," and therefore, as a free man, I take pride in the words 'Ich bin ein Berliner'."
Those last four words meant “I am a Berliner”.
The president's eight-hour visit came at a critical stage of the Cold War, with Berlin on the front line.
It was only a year since the United States and Soviet Union had nearly gone to war in the Cuban missile crisis, and two years after East Germany's communist regime had built the Berlin Wall dividing the city in two.
Lochner's daughter said he died suddenly overnight Saturday from pulmonary embolism, or a clot in the lungs.