Tom Branson was a central character on the series, Downton Abbey. He was played for most of the series run by actor Allen Leech.
From Chauffeur to Gentry
A native of Bray, County Wicklow, Ireland (an area located outside of Dublin), Tom Branson was first introduced to Downton Abbey in the first series (season) as the Crawley family's chauffeur.
He was also a very strident socialist, who was not very accepting of the gentry and their stranglehold on the world.
We are introduced to him in the fourth episode of the first series. He became the new Chauffeur after the previous one, Taylor, would move on and open up a tea shop. While employed there, he would fall in love with Lady Sybil Crawley, whom he discovered was just as political as he was.
After he tried to go off to war (he was refused to be drafted because of a heart murmur), he would finally get Sybil to accept his proposal of marriage. They would elope to Gretna Green (today which would be illegal, as that ended in the 1940s), with only her sisters to witness. A man named Starke would replace Tom as the family's chauffeur.
He and Sybil would return for Lady Mary Crawley and Matthew Crawley's marriage. He would be named best man after Larry Grey, a spiteful former suitor of Sybil's, tried to spike his drink with a drug that made him drunk.
Tom and Sybbie
Soon, he would become the father of a daughter, Sybil Branson II. Soon after her birth, her mother would die of Eclampsia. This would thrust Tom into becoming both mother and father to his newborn baby daughter (a rarity in those days).
He threw himself into it with a vengeance, as he was the only parent Sybbie had. It was clear to everyone that he adored his daughter and to him, the sun rose and set on her. He cherished the times that he and Sybbie could walk the grounds of the abbey and spend time together as father and daughter.
In a way, which would sometimes aggravate Sybbie's nanny, he would sometimes try to sneak into the nursery and kiss his little girl good morning, reminding him of when his mother would do the same to him and Kieran.
He would work hard to teach Sybbie about her Irish heritage (she was half-British, from Sybil's side of the family and half Irish from Tom's side), when she grew up.
Tom's life after Sybil
Tom would be the target of a crush by conniving housemaid later Lady's maid, Edna Braithwaite, but her scheme would not come to anything, as she would be sacked by Mrs. Hughes, one of Tom's friends from his days as a chauffeur, after trying to trap him into marriage.
He would later fall for a teacher named Sarah Bunting, who was just as much of a socialist as he used to be.
His political beliefs used to annoy his father in-law, Robert Crawley, but as time wore on, he realized that he would become very fond of him.
His mother in-law, Cora Crawley was more amenable to him, and was more compassionate towards him. She loved him the moment that he married into the family. It was she who would coin the name "Sybbie" for her eldest granddaughter, and she would bond close with her, as she was the most tangible link to her late youngest daughter.
As a christening gift from his late and beloved Sybil, Tom would be named the new Estate agent (the idea would be the brainwave of Violet Crawley).
At the request of Sybil, Sybbie would be christened as a Catholic, like her father. Her godparents would be her aunt Mary, and her uncle Kieran.
Interestingly, Sybil's granny, Violet, would grow to love him as she felt him to be the most practical of everyone in the Abbey. Her reasoning that Tom would make a wonderful agent was that due to his background, he had the most practical experience as a farmer. She also saw him as the calm and sensible voice of reason of the family.
After Sarah Bunting mercifully left Downton, he would later catch the eye of (and vice versa) of a woman named Laura Edmunds. They would meet at a racing event at Brooklands.
Laura was the editor of his sister in-law, Lady Edith Pelham's magazine, The Sketch. To Tom, he had come a long way from his beginnings as a outspoken and very socialistic chauffeur.
At first, he would be dealing with many crises of where he was, especially with the crafty Edna undermining him. It took his friend, Mrs. Hughes, to make him see that he was the bridge between the upstairs family and the servants.
He would leave Downton for a time when he and Sybbie would move to Boston to live with one of his cousins, but they would eventually come back to Downton to live there for good, when they realized that they were home, and Downton would ALWAYS be their home.
They would come to the wedding of Carson and Mrs. Hughes, and surprised everyone in the village with their appearance, and a happy and touching reunion between the family ensued.