A somewhat literary or old-fashioned word for a person on a journey, often with a nuance of being an outsider or someone passing through. In modern Japanese, 旅行者 is more common for 'tourist', while 旅の者 carries a more poetic or historical feel.
The villagers warmly welcomed the traveler.
The traveler sought lodging for the night.
Compound of 旅 (tabi, 'journey') + の (possessive particle) + 者 (mono, 'person'). The exact historical derivation is uncertain, but the construction follows a common pattern for describing a person by their role or state.