The Cheyenne Mountain Zoo lost one of its gentle giants over the weekend.

The zoo’s 15-year-old male giraffe, Mashama, died “somewhat unexpectedly” around 1 a.m. on Sunday, according to a news release.

Officials said Mashama was experiencing “sporadic off days” and went through bouts of lethargy and decreased appetite over the last few months, but he had more good days than bad ones.

According to the zoo, it was unclear what was causing these “off” days, as no patterns or causes were evident.

Mashama was born at the Cheyenne Mountain Zoo and was just weeks away from celebrating his 16th birthday, which is the median life expectancy for a male giraffe in human care.

His light-colored coat made him easy to identify, as well as the unique way he’d chew with his mouth wide open, the zoo said.

Nicknamed “Uncle Mashama” by fans, Mashama was one of the tallest giraffes in the herd and was known for being playful and gentle with new calves, the zoo said.

“He loved the babies and the babies loved him,” said Amy Schilz, senior animal behaviorist. “Young calves would follow him around and peek out from under his huge legs. They must have felt safe with him.”

Schilz worked with Mashama for 13 years, according to the zoo.

“He’s always been so gentle,” she said. “He was eager to please and eager to train. I’ll remember him as a calm, steady and gentle soul who absolutely loved training.”

As a “pioneer” in giraffe husbandry care, Mashama would participate in training and treatment sessions with his care team.

He would participate in blood draws, contributing to the Giraffe Plasma Bank that would supply emergency blood and plasma to giraffes across the country, the zoo said.

“He saved many calves’ lives through this contribution, and allowed veterinarians to learn more about giraffe blood testing, which continues to serve giraffes in human care and in the wild,” the release stated.