Long before its history was marked by the sound of bullets, thousands of fragrant flowers and crowds grievously singing “Imagine,” the Dakota was just another historic Manhattan co-op where among its famous inhabitants lived a musician named John Lennon.

Before he was gunned down in front of the building 30 years ago Wednesday, he was the seventh-floor resident who brought sushi to the building’s October potluck. He was known as a protective father and an enterprising real estate collector, irking a few neighbors by buying up five apartments in the building.

One of the many quirks and privileges of living in Manhattan is finding neighbors who are famous poets, celebrated scientists and aging jazz musicians. It was no different for residents at the Dakota, who grew used to seeing the former Beatle pass through the building’s entrance in his fur coat. What made the Dakota different from other buildings, besides its distinctive gothic design, was that so many residents were also celebrities that it afforded Mr. Lennon a certain degree of privacy....