The Zoo Atlanta family is mourning the death of its oldest male gorilla.
Ozzie, a Western lowland gorilla, was found dead in his enclosure by his care team at the age of 61 on Tuesday. He was the third-oldest gorilla in the world and the oldest at the zoo, the zoo said in an announcement.
"This is a devastating loss for Zoo Atlanta. While we knew this time would come someday, that inevitability does nothing to stem the deep sadness we feel at losing a legend," Raymond B. King, president and CEO of the zoo, said in a statement.
"Ozzie's life's contributions are indelible, in the generations of individuals he leaves behind in the gorilla population and in the world's body of knowledge in the care of his species. Our thoughts are with his care team, who have lost a part of their lives and a part of their hearts."
While Ozzie's cause of death is not yet known, a necropsy — the animal equivalent of a human autopsy — will be performed.
RELATED VIDEO: First-Ever Gorilla Born at Cleveland Zoo in its 139-Year History
Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.
The statement noted that Ozzie showed decreased appetite last week, and went on to present symptoms including facial swelling, weakness, and inability to eat or drink earlier this week.
The only surviving member of the original generation of gorillas who arrived at Zoo Atlanta with the opening of the Ford African Rain Forest in 1988, Ozzie made zoological history in 2009 when he became the first gorilla in the world ever to participate in a voluntary blood pressure reading.
Ozzie is survived by four children, one granddaughter and two great-grandchildren, all of whom live at Zoo Atlanta. His legacy also includes children, grandchildren, and great-grandchildren living at other accredited zoos in the U.S. and Canada.
Western lowland gorillas are a critically endangered species.
"According to the International Union for the Conservation of Nature (IUCN), over a 25-year period, the combined threats of poaching, illegal hunting for the bushmeat trade, habitat loss and emerging diseases have reduced western lowland gorilla populations by 60 percent, with declines of as much as 90 percent in some parts of their range in western Africa," the statement noted.
In June of last year, Ozzie celebrated his 60th birthday at the zoo, notably enjoying a multi-tiered ice "cake" full of frozen fruit and some extra love from staff.