General term for a person who climbs mountains, from casual hikers to serious alpinists.
See also: 山行者
The mountain climbers left the mountain hut early in the morning.
This mountain is popular with many climbers.
登山者 focuses on climbing mountains (often technical or summit-focused), whereas トレッカー emphasizes multi-day walking treks through trails.
Compound of 登山 (tozan, 'mountain climbing') + 者 (sha, 'person').