Happy, a Bronx Zoo elephant who gave researchers new insight into the animal’s behavior and became the crux of a closely watched animal rights case, has been euthanized at age 55, the zoo said Wednesday.

The Asian elephant was put to sleep Tuesday at the zoo where she lived for almost a half-century. Zoo officials said some age-related conditions accelerated in recent weeks, and she showed signs of a falloff in kidney or liver function. A necropsy revealed arthritis and large, inoperable uterine tumors that are impossible to diagnose in elephants through exams or imaging, the zoo said.

“She was a wonderful elephant,” interim zoo director Craig Piper said in an interview Wednesday, as heavy-hearted staffers absorbed the loss of an animal some had tended for over 30 years. “She served as a tremendous ambassador for elephants and for elephant conservation.”

Since Happy’s death, the zoo’s 57-year-old Patty is the last elephant on exhibit in the United States’ largest city. The zoo’s parent institution, the Wildlife Conservation Society, decided 20 years ago to stop acquiring pachyderms.

Born in the wild in Asia, Happy was brought to the U.S. as a 1-year-old. She was named for a character from “Snow White and the Seven Dwarfs” before arriving at the zoo in 1977.