How has London implemented character within "To Build a Fire?"

Like most good character building, London uses a mixture of direct and indirect characterization to build the character of the man. Additionally, London makes more use of indirect characterization than direct.  

Direct characterization is when the author expressly tells readers details about a character. In "To Build a Fire," this occurs when the narrator tells readers that the man doesn't have the ability to imagine.  

The trouble with him was that he was not able...

Like most good character building, London uses a mixture of direct and indirect characterization to build the character of the man. Additionally, London makes more use of indirect characterization than direct.  

Direct characterization is when the author expressly tells readers details about a character. In "To Build a Fire," this occurs when the narrator tells readers that the man doesn't have the ability to imagine.  

The trouble with him was that he was not able to imagine.

A bit later, the narrator also tells readers that the man is observant:

Empty as the man’s mind was of thoughts, he was most observant. He noticed the changes in the creek, the curves and the bends. And always he noted where he placed his feet.

The above quote contains a bit of indirect characterization as well. Indirect characterization occurs when an author shows readers what kind of person a character is through the character’s thoughts, words, and deeds. This requires readers to make inferences about a character. The above character description doesn't tell readers that the man is careful about his actions, but it is indicated by the fact that he takes the time to note where he will be placing his feet.  

Another character trait that readers can get about the man from indirect characterization is that he is stubborn and used to doing things his own way no matter what anybody else says. In a bit of a flashback, the narrator tells readers that the man was told not to go out alone in weather as cold as it is. The man ignores this advice believing that he is completely capable of handling anything that nature throws at him. I believe the following quote even paints the man as pompous:

He remembered the advice of the old man on Sulphur Creek, and smiled. The man had been very serious when he said that no man should travel alone in that country after 50 below zero. Well, here he was; he had had the accident; he was alone; and he had saved himself. Those old men were rather womanish, he thought.