Here's the breakdown:
* Who: This is a pronoun, functioning as the subject of the verb.
* Roamed: This is the past tense of the verb "roam".
Together, "who roamed" forms a simple sentence fragment, missing a subject.
Examples of how it could be used in a full sentence:
* Who roamed the forest?
* It was the wolf who roamed the forest.
* The children, who roamed the beach, found a beautiful seashell.