When Charles Kane reaches the age of legal maturity, he takes full control of his fortune and tells Mr. Thatcher at the bank that's he's not interested in his primary sources of income like mines and oil wells. Instead, he writes to Thatcher to say,
KANE: One item on your list intrigues me, The New York Inquirer, a little newspaper I understand we acquired in a foreclosure proceeding.
From this point on, Kane almost completely ignores the rest of his fortune to focus on running his newspaper and using it to critique the wealthy class of America—which he is also a part of.
At its heart, The Inquirer represents Kane's young ambitious dreams of making a real difference in the world and helping out poor people. When Mr. Thatcher confronts him about his war on the upper class, Kane simply answers,
KANE: I am the publisher of The Inquirer. As such, it is my duty, I'll let you in on a little secret, it is also my pleasure.
Over time, though, Kane's dedication to the public good gets crushed by the weight of his own giant ego. Over time, he stops worrying about what the poor think and believes he can simply tell them what to think. Eventually, Kane loses his newspapers in the Great Depression and that pretty much spells the end of his young idealism.
In fact, watching Kane's interaction with The Inquirer helps chart his growth as a character: from crusading upstart who wants to print the truth, to gossip-rag peddler, to bitter man who fires his friend because he dares to print a negative review of his wife's less-than-stellar singing.