In Mary Shelley's Frankenstein, Robert Walton is an explorer—the leader of an expedition to the North Pole. It is he that begins the story through letters he writes to his sister, Mrs. Margaret Saville. He is attempting to sail to other regions of the world—areas never before seen by another human. He wants to...
...tread a land never before imprinted by the foot of man.
Walton also wants to find a route over the North Pole that allows for shorter travel time to areas near the North Pole that presently take such a long time to pass with existing routes. In doing so, he would be benefiting all of mankind. (This is also what Victor wanted to do when he began his experiments: to benefit the entire world.)
...you cannot contest the inestimable benefit which I shall confer on all mankind, to the last generation, by discovering a passage near the pole to those countries, to reach which at present so many months are requisite; or by ascertaining the secret of the magnet, which, if at all possible, can only be effected by an undertaking such as mine.
It is a dangerous plan; one with which Walton becomes obsessed. While Walton is aware that he might die, but he does not seriously count the cost to those who travel with him.
Besides being the head of this expedition at the start of this Gothic tale of horror, Walton also serves several literary purposes as well.
Mary Shelley uses Walton as a foil to Victor Frankenstein.
[A foil is a] character that serves by contrast to highlight or emphasize opposing traits in another character.
In other words, by comparing Walton and Victor, we see two very similar men who want to attempt what has never been done before to be of service to humankind, to the point of obsession. In comparing the two men, we also see significant differences. It is in this way that the reader is able to view the choices of each man and recognize how the decisions of each affect the outcome of each man's life and that of those around them.
By the time Victor chases the creature to the North Pole, Walton has already arrived. Soon he is in dire straits. Trapped by "mountains of ice" that makes it impossible to move, his ship is in jeopardy, as are all hands aboard. If Walton continues, everyone may well die. When he is found near death, Victor's story becomes the catalyst for change, the motivation for Walton to make an ethical and wise choice. Whereas Victor has lost everything and everyone he has ever loved, Walton can make a decision to save himself and others. Victor warns Walton:
...learn my miseries, and do not seek to increase your own.
Walton is also the person to whom both Victor and the creature tell their stories, so that the reader is able to know not only what has driven Victor to such disaster and devastation, but also to learn from the creature its motivation for acting as it did.
While Walton may seem a singularly minor and unimportant character, he is a cloudy reflection of the title character of Victor Frankenstein. Comparisons between Walton and Victor provide the reader with a deeper understanding of Victor's folly and the fatal danger of his obsession. Walton also allows the reader to learn important information about Frankenstein and the monster he created, and a better understanding of the author's messages to the reader.