John Bradford, 62, died after being charged by a 41-year-old elephant, KOLR-TV, Springfield, reported.
The elephant, named Patience, has been a part of the zoo since 1990.
Zoo spokeswoman Cora Scott said other workers were with Bradford -- a 30-year employee at the zoo who was feeding the elephants at the time of the attack -- because Patience has a history of aggressiveness.
Paul Price, a friend of Bradford and former zoo worker, told the Springfield News Leader Bradford "had a great deal of respect and love for [elephants] and cared about the conservation," and helped build the zoo's elephant program.
"He was always aware of dangers and everything and was instrumental in developing the elephant management program at the zoo at the national and international levels," Price told the newspaper.
Police said Bradford had no immediate family in the area, but his brothers were notified of his death.
The zoo was open to visitors, the News Leader reported.
There was no initial word on whether any action would be taken against the elephant.
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