Ranger Smith is a supporting character in the Yogi Bear media from Hanna-Barbera. As his name suggests, he is the park ranger for Jellystone (and a former US Army soldier), where Yogi, Boo Boo and Cindy Bear live. He is strict and by-the-book, which usually brings him into contact with Yogi's constant antics.
Don Messick voices Ranger Smith in the vast majority of his appearances. Don gives Ranger Smith a quiet, yet stern voice that can be commanding but also humourous at the same time.
For Yo Yogi!, a show which features our beloved HB characters in a younger form, Greg Burson voices Officer Smith. There's nothing bad, per se, about Greg's performance. I just don't find it to be very special.
For Spumco's Ranger Smith short and Boo Boo Runs Wild, Corey Burton puts on the ranger hat (the... vocal hat, that is. [I really have to stop trying to make that joke work.]) Corey is probably the best VA to get to try and take over from Don Messick, as Corey's natural voice is a pretty decent match already. Although I do find that his is a bit gruffer than Don's.
Tom Cavanagh reprises his role from the live-action film for the video game adaptation. Now, obviously Tom wasn't trying to emulate Don, Greg or Corey in his portrayal, and was instead basing it (logically) off of his own live-action performance. It's not a bad role in its own right, it's just not anything special when you think of "Ranger Smith".