Mr. Dick is an older man living with Miss Betsey in her cottage at Dover. He is mentally disabled: he cannot look after himself. He is also about the kindest, most loyal guy out there – he thinks Miss Betsey is the most wonderful woman in the world, he really takes to David, and he also truly admires Dr. Strong.
Mr. Dick has a pretty tragic back-story: when his father died, his will requested that Mr. Dick's brother look after Mr. Dick. But Mr. Dick's brother was ashamed of him, and refused to let Mr. Dick share his house. So, he sent Mr. Dick away to an asylum – which, in the nineteenth century, were brutal, awful places where patients were frequently mistreated. So, Mr. Dick grew very ill. Miss Betsey rescued Mr. Dick and took over his guardianship.
Ever since Miss Betsey stepped in, Mr. Dick has been living happily with her. But he can't entirely forget his earlier abuse at the hands of his brother. So every day, Mr. Dick settles down to work on "his Memorial," a long speech praising some lord or other. But no matter how hard he tries, King Charles the First (1600-1649, an English king who literally lost his head in the English Civil Wars) keeps creeping in to the Memorial. Miss Betsey tells David that King Charles the First is Mr. Dick's symbol for his own mental and physical troubles:
"[King Charles the First] is his allegorical way of expressing it. He connects his illness with great disturbance and agitation, naturally, and that's the figure, or the simile, or whatever it's called, which he chooses to use. And why shouldn't he, if he thinks proper?" (14.59)
Miss Betsey is really kind to Mr. Dick, but when David arrives, his life gets even better: now, he has a companion with whom he can fly kites instead of constantly adding to his Memorial. And when David goes to school at Canterbury, Mr. Dick travels from Dover to Canterbury every Wednesday to visit him. Mr. Dick becomes close friends with David's headmaster, Doctor Strong. He believes that Doctor Strong is the finest scholar that ever lived and listens patiently to Doctor Strong reading out from his Dictionary.
When Miss Betsey goes bust and moves in with David in London, Mr. Dick accompanies her. They rent him another little room. But Mr. Dick isn't satisfied with being unable to help Miss Betsey in her time of need. He insists that David find something for him to do. It's Traddles who has the brilliant idea of using all of Mr. Dick's experience writing.
In these days before copy machines, all documents had to be copied out by hand. So Traddles takes his legal documents to Mr. Dick to be copied out and pays him by the page for his completed work. David and Traddles also come up with the idea of having a spare sheet of paper next to Mr. Dick as he is copying so that, the minute King Charles the First starts creeping into his writing, Mr. Dick can write about him on this other sheet of paper and leave his documents clean.
Mr. Dick is really happy to be able to help Miss Betsey in some way – in much the same way, actually, that David repays Miss Betsey's adoption by supporting her when Mr. Wickfield loses all of his money. There's definitely a quid-pro-quo moral system going on here: if you do me a favor, I'll do you one, Dickens seems to be saying.
Mr. Dick has one other major role to play in the unfolding of this novel. His friendship with Doctor Strong continues to the days when David is working as Doctor Strong's secretary at his house in Highgate, London. Mr. Dick notices that there is some kind of strain between Doctor Strong and his wife (and for details on that, check out the what we have to say about Mrs. Annie Strong and Doctor Strong). So, Mr. Dick decides to bring them together at the right time. He announces this plan to David in really intriguing terms:
"A simpleton, a weak-minded person [...] may do what wonderful people may not do. I'll bring them together, boy. I'll try. They'll not blame me. They'll not object to me. They'll not mind what I do, if it's wrong. I'm only Mr. Dick." (45.59)
What Mr. Dick is pointing to is that, as a mentally disabled man, he is outside the usual social structures of Dickens's novel: "They'll not blame me. They'll not object to me." In some sense, Mr. Dick is outside of class, so he has a freedom and flexibility to interact with people that others (including Miss Betsey and David) do not have. And Mr. Dick is aware of this power he has; he uses this social flexibility to bring Mrs. Strong into the room where her husband is drafting his will at just the right time. (We can compare Mr. Dick's social mobility to Miss Mowcher's.)