Yi Tien Cho, nicknamed Mr. Willoughby by Jamie, is a Chinese exile living in Edinburgh. Even more of a duck out of water than Claire, he can do acrobatics, has a sexual fetish for women's feet and a low tolerance for alcohol, none of which endears him to the local population. Mr. Willoughby has some knowledge of healing using Chinese medicine such as Baoding balls and acupuncture.
Yi Tien Cho was a Mandarin – a bureaucratic scholar in the government of Imperial China. He was gifted in the art of composition and was taken under the wing of another Mandarin, Wu-Xien, who recognized his talents. He rose rapidly through the ranks, achieving eminence before his 26th birthday, and his poetry was noticed by the Emperor's Second Wife, who requested that he become part of her household. This was a great honor, but all servants of the royal wives must be eunuchs. It was extremely dishonorable for anyone to refuse this request, but Yi Tien Cho had fallen in love with womankind, and did not want to lose his manhood. On the Night of the Lanterns, when the streets were crowded and the watchmen distracted, Yi Tien Cho disguised himself as a pilgrim and left the city. He was almost caught the next day, as he had forgotten to cut his fingernails, and still had the long nails of a Mandarin. He managed to escape his pursuers, and afterward destroyed his nails. Eventually he made it to a seaport and stowed away on the ship with the most barbarous looking crew, working on the assumption that they would be sailing the farthest from China. The ship was the Serafina, bound for Edinburgh.
He arrived in 1764 and lived on the docks, stealing food and alcohol, and was close to death when Jamie Fraser found him. Jamie took him under his wing and renamed him Mr. Willoughby, as his Chinese name sounded like a coarse word in Gaelic if mispronounced.
In 1766, Jamie is late meeting Mr. Willoughby on the day that Claire returns, and finds him drunk in the basement of the World's End tavern. Jamie rescues him from the irate tavern occupants, and he, Claire and Mr. Willoughby go to Madame Jeanne's brothel. The following day Mr. Willoughby apologizes to Claire for thinking she was a whore, acknowledging her as Jamie's "most honorable First Wife."
Later that morning, Mr. Willoughby is drinking again. When he is quite drunk, he finds Claire on the stairwell in the clutches of a man she believes is an exciseman. Mr. Willoughby tells the exciseman to release Claire; when the man fails to comply, Mr. Willoughby shoots and kills him. Fergus comes running and throws Mr. Willoughby down into the cellar.
About a week later, Mr. Willoughby travels with Fergus to the cove where the rendezvous with the smuggling ship is to take place, meeting up with Jamie, Claire, Young Ian and Jamie's men. Just as the ship is about to reach the shore, excisemen burst from their hiding places in the sand and the smugglers take flight, but Mr. Willoughby is grabbed. Jamie tells Ian to take Claire to safety and he heads down to the beach to rescue Mr. Willoughby.
Mr. Willoughby accompanies Jamie and Claire to France when they seek Jared's help in getting a ship to find Ian after he is kidnapped from the seal's island. Claire goes shopping for medical supplies with Mr. Willoughby, who proves surprisingly knowledgeable about herbs. They run into the Reverend Archibald Campbell, who eyes Mr. Willoughby with distaste. The Reverend Campbell explains that he is still traveling to the West Indies with his sister, but had some urgent business to attend to in France first. When the Reverend goes on his way. Mr. Willoughby tells Claire that he has seen the Reverend at Madame Jeanne's brothel, engaged in unholy behavior.
Once on board the Artemis, Mr. Willoughby keeps watch over Jamie by stationing himself outside Jamie's cabin while the latter is crippled by seasickness. Mr. Willoughby mentions to Claire that he has some Chinese medicine that will help, but that Jamie has refused to have it. Claire mentions in a very loud voice all the terrible things that can happen to a person constantly dry wretching, such as twisted testicles that have to be amputated, and Jamie gives in and allows Mr. Willoughby to treat him with his acupuncture needles. Fortunately for Jamie, the treatment works.
The crew learns of Mr. Willoughby's perverted fetish for women's feet and they regard him as a despicable heathen. This is not helped by the fact that Mr. Willoughby regards them in the same way. The seamen attempt to bully him but Jamie ensures this doesn't happen. One day while the crew are engaged in killing a shark to eat for dinner, Mr. Willoughby spies a pelican in the water and jumps overboard to capture it. Jamie jumps in after him and the crew manage to bring them both aboard before the sharks can get to them. Mr. Willoughby names the pelican Ping An and trains it to catch fish for him. With the pelican staying close to Mr. Willoughby, the crew no longer bother him. Mr. Willoughby tells the crew of the Artemis his story of how he came to be in Scotland. He is filled with a great sense of what he has lost and what his decision has cost him. He wonders whether the sacrifice he made was worth it.
He stays with the Frasers through a few more trials at sea, eventually accompanying them to a ball held at the governor's palace on Jamaica. He wears a black cap decorated with a new piece of coral ornament that Jamie gave him, an ornament signifying his former position in China. The guests at the reception are intrigued by him, particularly one Mina Alcott, who enjoys Mr. Willoughby's attentions.
Some little time later, however, Claire discovers the widow Alcott lying dead in a retiring room, and a trail of small, bloody footprints leading away and out of a window. Mr. Willoughby has disappeared, and the authorities hunt the island for him. Claire does not see him again until she returns to Rose Hall and faces off with the Reverend Archibald Campbell, whom Yi Tien Cho – having reminded his audience of his real name, and insisting upon it – accuses of murdering women in Edinburgh, and doing the same to Mina Alcott.
These revelations fit with what Claire knows, and she turns her gun on the Reverend, who in turn exclaims that it was Mr. Willoughby who betrayed Jamie to Sir Percival, resulting in the confrontation at Arbroath the previous autumn. Claire is momentarily frozen by the allegations but keeps her gun trained on the Reverend, who suddenly begins to charge at her before Yi Tien Cho uses his bag of Baoding balls to strike a fatal blow on the Reverend's head.
As the Reverend lies dying on the floor, Claire asks Yi Tien Cho if it's true that he betrayed Jamie. With little apparent emotion, Yi Tien Cho speaks of white men as if they are ghosts, and how Jamie, by learning his language, giving him a new name, and taking him under his protection, had eaten Yi Tien Cho's soul. He eventually explains vaguely that a man had come to the tavern asking about "Mac-Doo" and Yi Tien Cho told him yes, he knows him. He trails off, saying that it doesn't matter what he said to the man. His parting words to Claire are that his life debt is paid: Jamie saved Yi Tien Cho, and he now spares Claire's life. He disappears through the window, and the Frasers never see him again.
Yi Tien Cho says that his name means "Leans Against Heaven."
Chinese names tend to place surname ahead of given name, by which "Yi" is his surname. However, as he has been living in a society where surname is placed last, he might have accommodated as such, by which his surname would be "Cho".
Yi is from the Chinese 倚 (yǐ) meaning "to lean". This is a rare Chinese surname.
Tien is from the Chinese 天 (tiān) meaning "sky; heavens; heavenly; celestial".
Cho may be 愁 (chóu), meaning to worry, be anxious. In the context of his entire name, this character does not add or augment the meaning of the preceding 2 characters, but confers a slightly poetic quality to his name. As a possible surname, Cho may be a romanization of 趙 (Zhao), 曹 (Cáo), or 卓 (Zhuo).
Willoughby is a habitational name from any of the various places called Willoughby, for example in Leicestershire, Lincolnshire, Nottinghamshire, and Warwickshire. They are named from an Old English wilig "willow" + Old Norse býr "farm, settlement", or perhaps in some cases from wilig + Old English beag "ring".