@bradenslen SpenSer. "With an S. Like the poet."
I recommend starting with the second one, "God Save the Child," (1974), by Robert B. Parker, and then work forward. There are 45+ books in the series, counting the ones written by Ace Atkins after Parker's death. So that'll keep you busy for a while. :)
The first book, "The Godwulf Manuscript," is by the author's own admission a middlin'-quality Raymond Chandler pastiche. Parker doesn't find his -- and Spenser's -- true voice until the second book.