John William “Jack” Casady (born April 13, 1944) is an American bass guitarist, best known as a member of Jefferson Airplane and Hot Tuna. Jefferson Airplane became the first successful exponent of the San Francisco Sound. Singles including “Somebody to Love” and “White Rabbit” charted in 1967 and 1968. Casady, along with the other members of Jefferson Airplane, was inducted into the Rock and Roll Hall of Fame in 1996.

Casady was born in Washington D.C., the son of Mary Virginia (née Quimby) and William Robert Casady. His father was of half Irish Protestant and half Polish Jewish ancestry. His mother was a relative of aviator Harriet Quimby; some of her family had been in North America since the 1600s.

First playing as a lead guitarist with the Washington, D.C.-area rhythm and blues band The Triumphs, he switched to bass during his high school years, and while still underage (and with a forged I.D.) played the Washington D.C. club scene, backing artists such as Little Anthony and the Imperials.