When the Walker Tower in Manhattan was converted to luxury condos, the developers celebrated the building’s designer, Ralph Walker, who once was heralded as the “Architect of the Century” but had faded from history.

The developers commissioned a book on his life and an exhibit of his work in the building’s lobby. The marketing campaign proved wildly successful. A condo at the building on West 18th Street sold for $50.9 million in 2014 and for four years held the record as the most expensive downtown condo sale.

Now,...