A person who follows a leader, ideology, or trend. Slightly formal; in casual contexts, フォロワー or 信者 may be used depending on nuance.
He was a devoted follower of the charismatic leader.
The number of followers of the new trend is rapidly increasing.
Compound of 追従 (following, pursuit) and 者 (person). The exact historical derivation is uncertain, but the word follows standard Sino-Japanese word formation patterns.