If you reconsider and take the entire noun phrase "one of those French composers", you will be correct. Make the noun phrase singular:
HB is a French composer who is famous for his operatic music.
HB is one French composer who is famous for his operatic music.
HB is one of those French composers who is famous for his operatic music.
That Barrie England's answer and mine are at odds merely illustrates that usage mavens disagree about how to parse this kind of sentence. I won't argue with Barrie's answer. He can, I'm sure, cite references to support his claim. I can too, and here they are (You must click on the link to see the entire entry):
One of those [plural noun] that is/are …
"One is one and all alone and ever more shall be so," goes the old Christmas song, but the fact that the singular one needs a singular verb can lead to confusion. In a recently published collection of language columns by William Safire, No Uncertain Terms, he wrote the following sentence (page 336):
"Conduct unbecoming an officer and a gentleman" is one of those phrases that sounds as if it comes out of Kipling. The sentence caused considerable stir (as such things go), for the verb "sounds" should really relate to the plural "phrases," not the singular "one." The sentence should probably read (underlining things for our purpose):
"Conduct unbecoming an officer and a gentleman" is one of those phrases that sound as if they came out of Kipling. The rare device for figuring out which verb to use in this construction is as follows: turn the sentence inside out:
There is a possible exception, however. In Burchfield's New Fowlers*, we find this example:
"Don't you think," said Bernard, "that Hawaii is one of those places that was always better in the past." (from David Lodge, 1991; my underline) Burchfield adds, "A plural verb in the subordinate clause is recommended unless particular attention is being drawn to the uniqueness, individuality, etc., of the one in the opening clause." In an earlier note, Burchfield writes: "Exceptions [to the rule that we use the plural verb] occur when the writer or speaker presumably regards one as governing the verb in the subordinate clause," and he gives another two or three examples, including "I am one of those people who wants others to do what I think they should."