Sentence:  For these or for similar reasons, Jack London seems destined to be more than simply an author; he will continue to grow into a legend; then he will be transformed into a symbol — the protagonist of the Pioneers; the original Native Son; a portent of a newer generation; the "Man on the road"; the Pal on the Trail; the eternal traveler, the <WSD>ongoer</WSD>, the forward marcher. 
Meaning of the word marked with <WSD> tags:  One who continues moving along a path or carrying on a tradition.