Mr. Greene is the publisher of the Norvelt News. We don't see much of him (only when Jack delivers the obituaries), but what we do see of him suggests that he's smart and perceptive. Jack shows us how a "cloud of smoke hung over his head like a cartoon thought bubble full of swirling, unformed thoughts" (16.33), a nice visual of his quick mind.
How quick? He's the first person in the town to put things together and suggest that maybe someone should look into all of the deaths (21.59). Mr. Green writes an editorial toward the end of the book, which questions Miss Volker's integrity as town medical examiner, and makes it easier for the police to label her as a suspect.
Now, we like Miss Volker, so we're not too happy about her being suspected for murder—but we have to point out that Mr. Green has a point. Miss Volker keeps insisting that the women have died of natural causes, but, well, they haven't. They've been poisoned. Mr. Green is the one to see that maybe the town needs a more up-to-date medical examiner.
And—because we're Shmoop—that leads us to the Larger Question. Is the character of Mr. Greene a way for author-Gantos to make a point about the importance of newspapers and reporting? Are reporters vital to the health of a community? Of a nation?
You might be thinking that this is a lot of weight to put on one character—but think about it: the columns he prints help Norvelt remember its history, and the history of the whole world. Without those columns, the town would have no public forum, no place where they could all learn about what's going on in their community and in their world. Considering that the novel ends with Jack composing himself a little "Day in History" column, we're going to go out on a limb and say that Mr. Greene might just be one of the most important characters in the book.