When forming the construction one of the [plural noun] who (or that) . . . , follow with a plural verb. Thus He is one of the authors who succeed and One of the things that are known. A verb, we know, must agree with its subject, and although writers often mistake the subject of this construction’s verb to be the singular one, the subject is the who or that that follows and reflects the plural noun (and leads the clause to which the verb belongs). It’s easiest to understand this logic by rewriting the sentence. Using my first example, rewritten, it would read: Of the authors who succeed, he is one.
While the strict logic of this construction should be maintained, many writers, both expert and novice, fail to do so. But the popularity of poor prose does not make it any better—it is still poor prose.