"The little fellow had been suffering from lymphoma and after twelve and a half years of life, his body could not fight off the illness," Pres. Bush said in a statement.
Barney lived in the White House with the Bush family for eight years, and the president wrote that he "guarded the South Lawn entrance of the White House as if he were a Secret Service agent."
Bush wrote, "Barney and I enjoyed the outdoors. He loved to accompany me when I fished for bass at the ranch. He was a fierce armadillo hunter. At Camp David, his favorite activity was chasing golf balls on the chipping green."
Barney greeted lots of people, and "was always polite and never jumped in their laps."
Bush called Barney a "faithful friend" who "never discussed politics."
Barney was 12 and a half years old.