The world's last male northern white rhino, Sudan, has died after "age-related complications," researchers announced Tuesday, saying he "stole the heart of many with his dignity and strength."

A statement from the Ol Pejeta Conservancy in Kenya said the 45-year-old rhino was euthanized on Monday after his condition "worsened significantly" and he was no longer able to stand. His muscles and bones had degenerated and his skin had extensive wounds.

The rhino had been part of an ambitious effort to save the subspecies from extinction with the help of the two surviving females.

"He was a great ambassador for his species and will be remembered for the work he did to raise awareness globally of the plight facing not only rhinos, but also the many thousands of other species facing extinction as a result of unsustainable human activity," said the conservancy's CEO, Richard Vigne.