expert; skilled person; veteran
Refers to someone who has acquired high proficiency through long practice or experience. Neutral and widely applicable across fields.
彼はプログラミングの熟練者だ。
He is an expert in programming.
This task requires a skilled person.
熟練者 stresses skill gained through practice, whereas 経験者 only indicates having gone through the experience, not necessarily mastery.
Compound of 熟練 (jukuren, 'skill, proficiency') + 者 (sha, 'person'). The word follows a common pattern for forming agent nouns.