The Magician's Nephew details his childhood, and the later books have him as an old wise professor.
In the films, he is played by Jim Broadbent.
Digory Kirke is a young boy, originally from Dorset, who came to London because his father fell upon hard times and had to join the military in India. To cap it all, his mother, Mabel, was also very ill and was gradually dying, probably of cancer.
Role in the books
The Magician's Nephew
Digory has just moved into a dingy part of London and is very depressed. He suddenly meets Polly Plumber, a neighbourhood girl, and the two become friends because of their shared love of adventures and horror stories. When Digory describes Uncle Andrew, Polly is taken because of his alleged horrifying attributes.
Digory and Polly set to exploring the attic, guessing at what Andrew is doing which is so secret and involves Andrew being scared. Digory suspects piracy and Polly suspects a mad wife shut away. When the two break in through the adjacent corridor they find themselves in Andrew's study! A horrifying episode follows when Andrew seduces Polly, and she, being taken to him, is tempted to take a magical ring from a cabinet, when she touches it, she is whisked out of existence.
Believing her dead, Digory yells at Andrew, but Andrew reveals all that's happened is that Polly was transported to "another world" which he says is not another planet but a whole other universe. Digory is taken by Andrew's revelation that he was a dark magician, and he learns Andrew made the rings with dust which he claimed came from Atlantis. But Digory is driven to taking a yellow and green ring (for transport there and back) and Digory ends up in what is actually a lovely place, the Wood Between the Worlds, far from the nasty places Andrew had been describing. Digory meets Polly, lazing around, and they find the longer they stay in the Wood, the more sleepy they get. Polly and Digory notice other pools, like the one they came out of, and reason each pool is an interdimensional portal. So they jump in using yellow rings and end up in Charn, an abandoned city in a post-apocalyptic wasteland.
In Charn, Digory gets alarmed and wants to go home to Earth, but Polly gets all adventurous and she decides to explore. Polly and Digory are careful in the abandoned city, and they soon find a Hall full of statues, or waxworks, of incredibly gigantic humanoids wearing magnificent clothes. One of them, the final one, is a gigantic woman which Digory says is the most beautiful woman he has ever seen. They find a Bell and a Hammer and a pedestal which has an inscription on it, which tempts Digory to strike the Bell or "bide the danger." Digory is so overtaken by the dark magic he strikes the Bell and the beautiful waxwork reveals itself to not be a waxwork, but a living woman, who strides to her feet and demands who awoke her. Digory says it was him, and the woman says that he is no magician, and it is another magician who sent them there. The woman says her name is Jadis, the queen of Charn, and she takes them both outside, and see the destruction of Jadis' world. Jadis explains she destroyed her world by killing all her people in a war and her own sister. Jadis then wants to come to Earth, and Digory and Polly tell her its boring, but Jadis insists, and she follows them there through the Wood (which is sickening to her) and into Earth.
On Earth, Andrew is captivated by Jadis, and he insists upon being her servant. Jadis scorns his reputation as a magician and says he's weak. Digory is shocked Jadis is loose in London and wants to protect his mother and the world from Jadis. Polly returns from her house as soon as she is able, and, after the wreckage of a fight involving half of London and a cabbie named Frank, Digory and Polly wrestle Jadis away back into the Wood. But Frank and Andrew come too along with Frank's horse.
In the next teleportation, they all end up in Narnia, at its creation. When they all see Aslan summoning everything into being, Andrew and Jadis are shocked, but Frank, Digory and Polly are attracted to him. Finally, when Aslan makes animals and gives them the ability of speech, Aslan also speaks and makes order in Narnia. He then explains to Digory he bought Jadis into Narnia but she fled and to find a fruit to protect Narnia. Digory is sent with Polly to find a fruit and they go on Frank's old horse, given wings by Aslan. During the journey they meet Jadis at the orchard where the fruit is, and she tempts Digory into taking an apple and eating it and becoming immortal. Digory says he'd rather live like everyone else, die and go to Heaven afterwards. Then he tells the Witch to piss off and they return to Aslan and give him the apple, protecting Narnia with a fruit tree formed from the apple's seed.
Aslan knows of Digory's mother and he gives Digory an apple from the tree, and tells him to give it to her. Digory returns home and they take the rings from Andrew at Aslan's orders and bury them. Then, after Digory gives his mother an apple, she recovers and gets well again.
The Lion, the Witch, and the Wardrobe
Digory makes a cameo appearance in this novel as a wise old professor who had a wooden wardrobe made of the tree he created from the apple seed. Digory is living a reclusive life and he adopts Peter, Susan, Edmund and Lucy from the war. Digory teaches Peter and Susan that not everything is as it seems and those who appear mad may be the saner ones. He also teaches them about other worlds and how things disappear and then reappear. He says to Lucy she will return to Narnia at the climax ending of the movie hearing of their adventures.
The Last Battle
During the war, Digory's house is bombed and destroyed. But he is in London at the time so he survives. Wanting to make contact with Narnia again, he decides to dig up the rings with Polly and he hires Peter and Edmund to dig them up posing as builders. They do a seance and contact King Tirian of Narnia, last king of Narnia. Then the next day, they are all in a train crash, which tragically kills everyone onboard, including Digory.
But his spirit ends up in Narnia, and they all reunite, fight the Last Battle against darkness, and end up in Aslan's Country (which is Heaven).
Digory was pretty cocky and arrogant as a kid but as a teenager and a man he got wiser and kinder, and more patient. He was very similar to Andrew as he began by believing only that which he could see, but then he learned otherwise. He was also similar to Edmund how he started as a complete fool, but then redeemed himself through Aslan.