Please give me a character sketch of Mr. Keith.

Listed in the book Representative Men and Old Families of Southeastern Massachusetts, Merton Spencer Keith, son of Benjamin Keith, was born on January 27, 1851, in North Bridgewater, which is now the city of Brockton. Keith entered Harvard College in 1868 and graduated summa cum laude in 1872 at the head of his class. His highest honors were in ancient languages.

Merton Keith became a teacher and was a member of the faculty at Professor George W. C. Noble's school in Boston. This school was a preparatory school where he worked for thirteen years. After he left this school, Keith became a private tutor who prepared boys for Harvard. About this fine teacher, one of his peers wrote,

Mr. Keith lives for his profession, his whole heart and soul being in his work, and he takes a deep interest in his pupils and their success. 

In Chapter XIX of Helen Keller's The Story of My Life, Mr. Merton Keith became a tutor for Helen. According to Miss Keller, he was instrumental in clarifying much for her. From February to July, 1898, Mr. Keith came from Cambridge to Wrentham twice a week in order to instruct Helen in algebra, geometry, Greek, and Latin. As he did so, Miss Sullivan interpreted his instruction for Helen.

Algebra and geometry were difficult for Helen to comprehend, partly because in her study of geometry she could not see the diagrams and realize the relation of the different parts to one another—even when she used wires that were pinned into position on a cushion. When Mr. Keith began work with Helen, she improved markedly. Helen wrote in her autobiography that his instruction was invaluable to her:

It was not until Mr. Keith taught me that I had a clear idea of mathematics. (Ch. XIX)

For eight months Mr. Keith worked with Helen. Under Mr. Keith's tutelage, Helen found mathematics interesting. She described her tutor as being able to "whittle" problems down so that she could understand, and he kept her interested. He trained Helen in the reasoning process and prevented her from jumping to answers that were inconclusive. Helen wrote of him,

He was always gentle and forbearing, no matter how dull I might be, and believe me, my stupidity would often have exhausted the patience of Job. (Ch. XIX)

With the expert assistance of this fine tutor, Helen Keller was able to pass all her entrance exams for Radcliffe College.

Additional Source: 

J.H. Beers and Co. Representative Men and Old Families of Southeastern Massachusetts. General Books LLC, 2010.