"It's always useful to have a mechanic
-- a nuts and bolts person" Said Harold Ramis.
"(Someone who is) honest, straight-ahead, enthusiastic. And
that really worked for Dan."
The shooting script describes Ray: "He is Venkman's colleague and best friend. A hard scientist with a good academic background, Stantz is a maverick who genuinely loves a challenge."
We get to see a good side of Ray's personality throughout the film. He is the balance between Venkman and Spengler that gives the movie an edge. Stantz is the guy who explains things to us in the film so we don't get lost. He is also a child at heart. We learn of Camp Waconda, what Mr. Stay Puft means to him, his religious beliefs, and the childhood home that his parents left him.