The article name, when first mentioned, should be in bold text. If a story title, it should additionally be italicised, as with An Unearthly Child. Alternate names for the topic should also be bolded. In most cases, any alternate name which is emboldened should also get a redirect.
Because emboldened text carries a meaning — namely, "this is the topic of the page" — bold text should be used sparingly in the rest of the article.
Bold text which appears within publisher's summaries, for instance, should be stripped — even though it may have appeared in the original printing of the text — because it causes visual confusion at the top of the page. Consider indenting — with the use of a preceding colon (:) — long passages of emboldened text found on back covers of books.
Similarly, working titles of stories should not be emboldened at any point in the text of the page, unless the titles are significant enough to warrant a redirect, and unless those titles are in the lead of the article. For instance, 100,000 BC is indeed emboldened at An Unearthly Child, because several sources consider it the correct name of the serial.