Robert Walton reveals much about himself through both direct and indirect characterization throughout the opening letters (Letters I-IV) of Mary Shelley's Frankenstein.
Walton is a determined man. His quest for the seat of magnetism is obsessive. In Letter I to his sister, Walton reveals his long time interest in science and discovery.
Six years have passed since I resolved on my present undertaking. I can, even now, remember the hour from which I dedicated myself to this great enterprise.
This quote shows Walton's determination. Later, in Letter III, Walton states his intent to be successful.
But success shall crown my endeavours.
Love of Family
The fact that Walton keeps writing to his sister shows his devotion to his family. Even Victor, as found out later in the novel, fails to write home over the many years he is gone (given his complete and utter obsession with reanimating life).
Walton, in order to tell Victor's tell accurately, states his intent to keep the tale as factual as he possibly can. He states the following in Letter IV.
I have resolved every night, when I am not imperatively occupied by my duties, to record, as nearly as possible in his own words, what he has related during the day.
One thing which Walton desires, almost as much as he desires to reach the pole, is friendship. Like his devotion to family, Walton's desire to have a friend is immediate. He wants to have someone who can understand his desires and share in his triumphs. Unfortunately, prior to Victor's arrival, Walton is alone among the men who help to pilot the ship.
But I have one want which I have never yet been able to satisfy; and the absence of the object of which I now feel as a most severe evil. I have no friend.