The country music world is mourning the loss of Glen Campbell, who died today at the age of 81. The country singer had struggled with Alzheimer's for years. He's best known for his hits "Rhinestone Cowboy," and "Gentle On My Mind," and his variety show "The Glen Campbell Goodtime Hour" on CBS. Campbell had several acting credits, including co-starring in 1969's "True Grit" with John Wayne and 1970's "Norwood" with Joe Namath. He released his last album, "Adios" this summer.