The sentence type of "Nathan, who never does anything wrong, did something wrong." is complex.
The complex sentence refers to the sentence which contains at least one dependent clause and an independent clause. A dependent clause is the clause which cannot stand alone in its meaning on the other hand independent clause refers to the phrase which can stand alone, though both have a subject and a verb.
Hence, in the above sentence, dependent clause is "Who never does anything wrong" and independent clause is "Did something wrong."
