Learn Russian: В этом романе убили главного героя. - In this novel the main character was killed.

Russian frequently avoids the passive voice (like "was killed") by using an indefinite-personal construction. By using the third-person plural verb убили without the pronoun они (they), the sentence focuses entirely on the action and who it happened to, rather than who did it. In English, this is most naturally translated as a passive sentence.

Why is главного героя in what looks like the Genitive case if it is the direct object?

It is actually in the Accusative case! For masculine animate nouns (living things like people or animals, such as герой), the Accusative case endings are identical to the Genitive case endings. Because the character is the direct object receiving the action of the verb, it takes this animate Accusative form.

Is роман related to the English word "romance"?

They are related, but роман is a classic "false friend" for English speakers. While it can mean a romantic affair, in the context of books and literature it simply means a "novel." If you wanted to specify a romance novel, you would say любовный роман.

Why translate герой as "character" rather than "hero"?

While герой does mean "hero" in contexts involving bravery, it is also the standard Russian term for a character in a book, movie, or play. The phrase главный герой is the normal way to say "main character" or "protagonist," regardless of whether that person is actually heroic.