I am confused by the relative pronoun in the sentence below. According to grammar rules, if there is a 'who' before a relative pronoun, then the relative pronoun should use 'that' to replace 'who'. However, here if the relative pronoun uses 'that', it lays a false scent with 'hat that'. So, which is acceptable, who or that?
Who was the boy with a conical hat ____________ (who, that) crawled through the ladder in this photo from 50 years ago?