Jack Hanna's long goodbye: How Alzheimer's is stripping away the man the world once knew

Jack Hannah @ The David Letterman Show 2

Letterman - Jack Hannah

Donald Trump on Letterman, May 21, 1992

Jack Hanna on "Late Night with David Letterman"

Unscripted: Jack Hanna regrets 1972 accident

Top Ten List presented by celebrity mothers—Letterman show

Johnny Gets Punched By A Baboon with Jim Fowler - Carson Tonight Show

Jack Hanna: Right decision was made to kill gorilla

Jack Hanna Bitten by a Beaver - David Letterman December 1988

Joaquin Phoenix's Infamous Appearance With Dave | Letterman

Animal Bloopers with Jack Hanna (1994) (VHS)

The Dog That Tried To Bite Dave's Face Off | Letterman

Jack Hanna's Into the Wild

Jim Carrey's First Appearance on Letterman, July 25, 1984

David Letterman: Dave is bothering everybody at McDonalds

Jarod Miller animal expert

Classic Dave - Jack Hanna, 1/5/88

1986 (Feb.) - Jack Hanna

David Letterman interview, Tonight Show with Johnny Carson - July 13, 1984