Martha Louise Hudson (née Sissons) is the landlady of 221B and 221C Baker Street. She rents 221B out to Sherlock Holmes and Dr John Watson. Mrs Hudson lives in the same building in a flat of her own.
Sherlock won his way into her good graces after ensuring that her husband was executed for a double-murder in Florida. Due to his assistance, she allows Sherlock and John to have the flat at a lower cost than what it is worth. According to John, it is in a "prime location".
Despite repeated declarations that she is not their housekeeper, she fusses over Sherlock and they share somewhat of a 'mother-son' relationship. Even Mycroft is far more casual than usual with her, and atypically flummoxed when he tells her to "for God's sake, shut up, Mrs Hudson!".
She often assumes that John and Sherlock are a couple, despite John's constant proclamations on the topic.
Sherlock mentions to John that she offers him a special deal on the rent because he helped her out by ensuring the conviction and execution of her husband in Florida. 
Mrs Hudson's character is further improved in the second series, as well as how much Sherlock values her. When Mycroft Holmes tells her to shut up, Sherlock is immediately provoked to snap at his brother (Which is one of the very few times that Sherlock is seen to have done so). Mrs Hudson also becomes more directly involved with a case when 221B is attacked by apparent CIA operatives looking for a video phone that Irene Adler has left in Sherlock's possession; when the agents torture Mrs Hudson trying to find the phone, the normally aloof Sherlock throws the agent responsible out of an upper-level window – apparently several times – and later (when John suggests for her own safety she takes a leave) reaffirms his affection for her by stating that "England would fall" if Mrs Hudson left Baker Street. It is heavily displayed that Sherlock violently assaulted the agent before throwing him out of the window
She is one of the three people who make up the full list of "Everyone you care about", each of whom Moriarty threatens to kill if Sherlock fails to commit suicide.
John Watson returns to Baker Street to visit Mrs Hudson, who is visibly upset at the lack of contact he has had with her since the two years of Sherlock being gone. She confronts him about how hurt she was, that for two years he never once contacted her, after all, they went through. She tells him she understands how difficult it was for him, to which Watson tells her how he let it slide, and it just got harder and harder to pick up the phone. Mrs Hudson and John return to the flat, revealing that she left it just as Sherlock had it. John tells her he is getting married, and Mrs Hudson asks what his name is. John assures her that it is a woman. Mrs Hudson is delighted at the news. Later when Sherlock comes back to Baker Street to show he is still alive, Mrs Hudson hears a noise and arms herself with a frying pan. She screams at the top of her lungs. 
After Sherlock has reclaimed his room a Baker Street, Mrs Hudson brings Sherlock his tea and excitedly talks about "the big day" – John's wedding. After Sherlock and John's stag party, she makes John a full breakfast (much to his nausea) and goes on about how different life will be once he is married. She reveals a lot more information about Mr Hudson (as she briefly mentions his first name is "Frank"), and that it was purely a physical relationship and she knew it would never last; however, she was completely unaware of his "other activities" until the police arrested him for "blowing someone's head off". It was revealed that he was running a drug cartel, and had relationships with many other women. Mrs Hudson was rather relieved once he was arrested. 
- "Family is all we have in the end, Mycroft Holmes."
- ―Mrs Hudson to Mycroft
Mrs Hudson is kind and caring, and she looks after Sherlock and John despite insisting that she is their landlady, not their housekeeper.
- In the "Unaired Pilot", Mrs Hudson owned the Speedy's Cafe shop, which was called 'Mrs Hudson's Snax n' Sarnies'.
- She has a bad hip, although it does not appear to impair her mobility, and uses what she describes as "herbal soothers" for the pain.
- She owns an expensive sports car. (When John asks how its possible, Mrs Hudson points out that "I'm the widow of a drug dealer; I own property in Central London; and for the last bloody time, I'm not your housekeeper!")
- She gives Sherlock tea in the morning; however, he thought it just "sort of happened" before the Sign of Three as he was never awake that early.
- Enjoys playing scratch-cards.
- Interestingly, the moments where Sherlock is provoked into rare and extreme violence or anger is when Mrs Hudson is insulted, or when her life is in danger.
- Is apparently a fan of Connie Prince. (She and John Watson enjoy 'trash telly'.) 
- Sherlock and John discuss buying her a laptop for Christmas so she does not have to borrow Mrs Turner's (John's Blog).
- It is implied by Sherlock that her husband was guilty of double murder and executed by lethal injection.
- A running joke throughout the series is she believes John to be gay. (This is dropped in Season 4, with his marriage to Mary.)
- Revealed by Charles Augustus Magnussen's information that her full name is Martha Louise Hudson (née Sissons), Widow. A semi-reformed alcoholic. Occupation: Landlady, a former exotic dancer. Her "pressure point" is marijuana. 
- During a cast Q and A, Una gave her opinions of what Mrs Hudson does for Sherlock. (Sherlock apparently eats rubbish unless Mrs Hudson cooks for him.)
- ↑ 1.0 1.1 1.2 Moffat, Steven (writer) & Hurran, Nick (director). (12 January, 2014). "His Last Vow". Sherlock (2010). Series 3. Episode 3. BBC One.
- ↑ 2.0 2.1 2.2 Moffat, Steven (writer) & McGuigan, Paul (director). (25 July, 2010). "A Study in Pink". Sherlock (2010). Series 1. Episode 1. BBC One.
- ↑ Moffat, Steven (writer) & McGuigan, Paul (director). (1 January, 2012). "A Scandal in Belgravia". Sherlock (2010). Series 2. Episode 1. BBC One.
- ↑ Thompson, Steve (writer) & Haynes, Toby (director). (15 January, 2012). "The Reichenbach Fall". Sherlock (2010). Series 2. Episode 3. BBC One.
- ↑ Gatiss, Mark (writer) & Lovering, Jeremy (director). (1 January, 2014). "The Empty Hearse". Sherlock (2010). Series 3. Episode 1. BBC One.
- ↑ 6.0 6.1 Thompson, Steve; Moffat, Steven; Gatiss, Mark (writers) & McCarthy, Colm (director). (5 January, 2014). "The Sign of Three". Sherlock (2010). Series 3. Episode 2. BBC One.
- ↑ Throughout Sherlock.
- ↑ Gatiss, Mark (writer) & McGuigan, Paul (director). (8 August, 2010). "The Great Game". Sherlock (2010). Series 1. Episode 3. BBC One.