https://www.imdb.com/title/tt0060182/
Married couple George Adamson and Joy Adamson have long lived in northern Kenya for George's work as the senior game warden of the region. One of George's primary responsibilities is to deal with dangerous animals that may be chronically threatening to humans, livestock and/or crops. It is in this vein that George and his staff end up killing a man eating lion and its lioness, resulting in their three young female cubs being orphaned. Although difficult to begin, George and Joy are able to wean and take care of the three cubs, who they adopt as pets. But soon, they know they have to provide a more suitable environment for the cubs, namely sending them to Rotterdam Zoo... that is except for the smallest, who they have named Elsa and to who Joy in particular has become attached as the emotional fighter among the three. As Elsa grows into lioness maturity, George and Joy provide her with greater freedom away from their property, which may get her into trouble as a largely tame animal. Ultimately, John Kendall, George's boss, directs them to send Elsa to a zoo like they did with her sisters, especially as with anyone in George's job he is soon being reassigned. Joy cannot bear the thought of Elsa being locked up for the rest of her life, believing that they can reintegrate her back into the wild instead, something that had never been done with a tame lion. John gives them three months to accomplish this task, which most specifically involves getting Elsa to be able to kill for food, other creatures which up to this point she has seen only as fellow playthings, and to be accepted by other lions, most specifically mate with and provide food for a male partner while standing up successfully to female competitors. —Huggo
So it would not be wrong to state that this was the start of reintroducing wild creatures back into the wild.
After several unsuccessful attempts at reintroducing her back into the wild, Elsa begins to get the idea of killing to feed herself. When she goes into season, the Adamsons make one more attempt to release her into an existing pride. They find a lion who seems to be receptive to her and set her loose. Unfortunately, the lion already has a lioness in his pride, and she attacks Elsa. This time, however, Elsa fights back and, after Joy fires off a shot, the three of them run off together. A year later, after being away in Britain, the Adamsons return to Kenya. They set up camp at the spot where they last saw Elsa and spend the next week looking for her, but she never shows. Forced to give up the search, they return to base camp to prepare to fly back to Britain. Suddenly, Joy hears lion sounds and is overjoyed to see Elsa come walking out the bushes accompanied by three cubs. After a fond reunion in which Elsa makes it clear that she hasn't forgotten them, her mate calls to her, and Elsa and the cubs join him. In a voiceover, Joy says, 'We saw her many times again...born free and living free. But to us, she was always the same...our friend Elsa.'
It does not get much better than that . . .
; Julia Child
