The New York Times is reporting that Susan Bay Nimoy, his wife, has confirmed his death as the result of end-stage chronic obstructive pulmonary disease. Leonard Nimoy publicly revealed the disease just last year and said it was the result of years of smoking.
In addition to his work on the Star Trek shows and movies, Nimoy was a successful movie director, voice actor, and host of the Ancient Mysteries TV series. He was a writer which included works of poetry and produced art works as well.
More info at NY Times. Leonard Nimoy, Spock of ‘Star Trek,’ Dies at 83 (Published 2015)