Captain Keller, Helen's father, becomes Annie Sullivan's ally toward the end of act 3. Captain Keller, rather than trying to fire Annie Sullivan from her position as Helen's teacher, finally gives her her first month's salary:

Keller: Miss—Annie . . . I've been waiting to give you this.

Annie:. . . What?

Keller: Your first month's salary. . . . With many more to come, I trust. It doesn't express what we feel, it doesn't pay our debt. For what you've done.

Earlier in the play, it seems as though Captain Keller has lost all hope that his blind and deaf daughter might ever communicate with language or be able to live a normal life. In act 1, Aunt Ev brings Mr. and Mrs. Keller's attention to an oculist, Dr. Chisholm, who is known for his "wonders" in helping blind people to see.

Captain Keller shows his hopelessness when he says he will not write to the doctor; he has talked to too many doctors and does not see the use:

Keller: The child's been to specialists all over Alabama and Tennessee. If I thought it would do good I'd have her to every fool dotor in the country.

Kate: I think the Captain will write to him soon.

Keller: Katie. How many times can you let them break your heart?

Kate: Any number of times.

From the beginning of the play, Kate has more hope that Helen might come to live a normal life. Captain Keller cannot imagine that any doctor (or any other person) might be able to teach or improve a girl who is both blind and deaf from early childhood. He is satisfied with keeping Helen content by letting her have what she wants. He doesn't want anyone to spoil her happiness.

Annie, who disrupts Helen's happiness by refusing to spoil her and allow her to always have her wishes, finds a way to communicate with Helen through sign language. Originally, Captain Keller despises Annie's methods since she disrupts Helen's happiness and contentment. Annie earns Helen's trust and eventually, through teaching her sign language, is able to teach her about the world. She does not lose hope on Helen because of her visual and auditory disabilities.

Keller soon sees the changes that Annie promotes in Helen in a short time. After leaving Helen alone with Annie in the little house a couple of weeks, he sees the drastic improvement in Helen's manners. (He already sees Helen's growth, even before Helen learns to communicate.)

Keller: It's like expecting a new child in the house. Well, she is, so -- composed, so -- Attractive. You've done wonders for her, Miss Sullivan.

Captain Keller becomes Annie's ally when he sees the benefit of trying to teach Helen new skills (such as communication), rather than simply trying to keep her content and happy by letting Helen always have her way.

As the play continues, Keller witnesses how Annie teaches Helen far more important things than social manners. He grows in admiration of Annie throughout the play.

At first, Captain and Mrs. Keller are uncertain about Miss Sullivan's methods in teaching Helen.  At times, Captain Keller wants to send Miss Sullivan back to Boston.  He does not believe that Miss Sullivan can truly help Helen, who is deaf and blind.

In Act III, Captain Keller begins to see Miss Sullivan and Helen making progress.  He sees that his daughter is responding to the teacher's methods.  Captain Keller expresses his gratefulness to Miss Sullivan, saying that she has "taken a wild thing, and given [them] back a child."

Captain Keller agrees to help Miss Sullivan by being consistent with Helen.  He plans to establish boundaries with his daughter.  He will no longer give in to all of Helen's whims.  In the past, Captain Keller and his wife had let Helen do almost anything she wanted.  For example, at mealtime Helen ate off of everyone's plates with her hands.