Jim Varney

From Pixar Wiki

Jim Varney was born in Lexington, Kentucky on June 15, 1949, and died on February 10, 2000. He is the voice of Slinky Dog in Toy Story and Toy Story 2. Pixar has said that his role as Slinky will now be played by Comedian Blake Clark a friend of Varney's who sounds very similar for Toy Story 3.