habitual offender; addict
Refers to someone who repeatedly engages in a particular behavior, often with a negative connotation. Can be used for criminal recidivists or for people with compulsive habits (e.g., gambling, substance use).
He is known as a habitual thief.
Compulsive gamblers find it very hard to quit.
中毒者 emphasizes physical or psychological addiction (e.g., drug addict, alcoholic), whereas 常習者 focuses on the habitual nature of the behavior, which may or may not involve addiction.
Compound of 常習 (habitual practice) + 者 (person). The exact historical derivation is straightforward; the word follows a common Sino-Japanese pattern for forming agent nouns.