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This centenarian is finally retiring.

Diego, a tortoise more than 100 years old, is credited with helping to restore the tortoise population in the Galapagos Islands, where a 40-year breeding program on Española Island has just wrapped up.

The Giant Tortoise Restoration Initiative, led by the Galapagos National Park Directorate and the Galapagos Conservancy, began in 1965 with the aim of repopulating the islands’ threatened tortoise species. At the time, only 14 tortoises — two males and 12 females — lived on Española Island.

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Diego returned from the San Diego Zoo to his island of origin in 1976 to join the original population in a captive breeding program. On Friday, the initiative's director, Washington Tapia, said there are 2,000 tortoises on the island.

"The island has sufficient conditions to maintain the tortoise population, which will continue to grow normally — even without any new repatriation of juveniles," Tapia said in a statement.

And Diego gets a lot of the credit; he is believed to be responsible for 40 percent of the island’s newly repatriated tortoises.

His contributions were recognized on Twitter after the GNPD and the Galapagos Conservancy announced the completion of the program.

This turtle is too dang cute. Diego!! ❤🐢🐢 pic.twitter.com/CBpp4wdK9w — Meredith ♐💋 Yes I'm 47! 💯 (@Mkf257) January 14, 2020

Another tortoise, "E5," is responsible for the other 60 percent of Española tortoises, according to The New York Times. But Diego has garnered attention for his "big personality" and for being "quite aggressive, active and vocal in his mating habits," James Gibbs, a professor of environmental and forest biology at the State University of New York in Syracuse, told the Times.

Giant tortoise species had seen the worst depopulation on the Galapagos Islands, and feral goats are the likely culprit. The Times reported that whalers likely introduced the goats to the islands as food nearly 200 years ago. The goats combined with a dearth of vegetation kept tortoises from thriving.

Goats were eliminated from Española Island by 1978 and from several other islands in the archipelago by 2006. And while the tortoise population has made major gains, it has a long way to go to grow to the size of its original population: between 200,000 and 300,000 tortoises.

For now, though, the 15 original breeding adults — including Diego — are expected to be released to their native Española Island in March following a quarantine process.