Mr. Wickfield is a lawyer and businessman living in the town of Canterbury, where David goes to school after running away from London to his aunt's house in Dover. Mr. Wickfield is the business manager for both Miss Betsey and Doctor Strong, David's new headmaster. When David comes to Canterbury for school, Mr. Wickfield offers to let David stay with him. Mr. Wickfield is mostly a good man at this point in the novel. We particularly like his concern about Doctor Strong's family life.
David is glad to stay with him: he likes Mr. Wickfield's house, the promise of more education, and Mr. Wickfield's daughter Agnes. For his part, Mr. Wickfield wants David to stay so that he can be some company for Agnes to keep her from getting unsatisfied with living with Mr. Wickfield. He comments to David: "You are company for us both. It is wholesome to have you here. Wholesome for me, wholesome for Agnes, wholesome perhaps for all of us" (16.79). So already, we're getting hints that something is wrong with Mr. Wickfield's household: he's angsting all the time about his daughter, and he is given to dark moods.
The first moment David meets Mr. Wickfield, David notices something about him that is going to prove to be Mr. Wickfield's fatal flaw: he has the red complexion and burst blood vessels in his face of someone who drinks way, way too much. Indeed, Mr. Wickfield is an alcoholic. Having lost his wife when Agnes was two weeks old, Mr. Wickfield has raised his daughter by himself. He is absolutely focused on Agnes, and he can't stand to part from her: he "must have her near [him]" (16.72). Out of sorrow for his wife's death and worry over his daughter (will she ever leave him?, he wonders), Mr. Wickfield drinks to drown his sorrows.
His awful clerk, Uriah Heep, takes advantage of Mr. Wickfield's moral weakness to attach himself to Mr. Wickfield's business like a leech. And the worst thing of all is that Mr. Wickfield can see what Uriah Heep is doing, but only once it's way too late to stop him. Mr. Wickfield knows that Uriah Heep plans to force Agnes to marry him, and there's not a darn thing Mr. Wickfield can do about it.
When Uriah Heep finally announces his wish to marry Agnes in front of David and Mr. Wickfield, Mr. Wickfield has a breakdown:
I have infected everything I touched. I have brought misery on what I dearly love [...] Sordid in my grief, sordid in my love, sordid in my miserable escape from the darker side of both, oh, see the ruin I am, and hate me, shun me. (39.153)
We find this moment fascinating for a number of reasons: first, we imagine it's pretty much the most awful thing ever to look at your daughter and know, beyond the shadow of a doubt, that you have ruined or are ruining her life. Mr. Wickfield isn't a bad guy, he's just a weak one, and the knowledge of what he's doing seems to be breaking his spirits even further.
Second, Mr. Wickfield often describes his love of his daughter as "sordid" (gross, vile, or selfish) and "diseased" (60.77). What exactly the nature of this diseased love is is never entirely clear. We just know that, in being so obsessed with keeping Agnes near him because she reminds him of her mother, Mr. Wickfield has left her open to the plots of Uriah Heep. Mr. Wickfield has given Agnes a great deal of pain in her life, all because he loves her too much to let her go out into the broader world.
Once Uriah Heep's plots have been exposed, Mr. Wickfield's name cleared, and all of the money paid back, Mr. Wickfield retires. Mr. Wickfield also quits drinking. It's after David returns from his trip abroad that he finds Mr. Wickfield a quieter, wiser, better man. Mr. Wickfield finally tells David about Agnes's mother.
Agnes's mother was a devoted wife who loved Mr. Wickfield dearly. But she also had a bullying, domineering father who absolutely rejected his daughter for marrying Mr. Wickfield against his wishes. His rejections finally broke Mrs. Wickfield's heart, and she died after Agnes was born. But until her death, Mrs. Wickfield did her best to hide her unhappiness from her husband because she loved him so much.
This self-sacrificing love reminds us an awful lot of Agnes herself. Even Mr. Wickfield notes that Agnes's whole life seems to have been shaped and altered by how her mother died. Again, the moral of the story (for the women of this book, at least) seems to be that complete self-sacrifice is the best moral code. Even if the man you're sacrificing for is not worthy, that's still what you have to do to be a truly good woman.