RACINE, Wis. (CBS 58) -- Nelson, an African penguin born at the Racine Zoo in March 2021, was humanely euthanized on June 3 after animal care staff discovered he was suffering from a terminal illness. He was 5 years old, according to the zoo.

Known by his orange band and a distinct hunched posture caused by a spinal infection he survived as a chick, Nelson is described by Racine Zoo staff as being among the zoo's most recognizable animals. He was also touted as the most personable, forming an unusually close bond with his keepers, who remembered him for stealing shoes, preening their fingers and testing the patience of his colony neighbors.

Nelson was survived by his twin brother, Ozzy, who hatched just two days after him.

The zoo noted that African penguins are critically endangered, and that Nelson's birth was considered a significant achievement for the species' conservation efforts.