conformist

Short definition from Wiktionary

Noun

1. 1
   Someone who tries to conform to the mainstream.
2. 2
   A noctuid moth (Lithophane furcifera)
3. 3
   In English history, a person whose religious practices conformed with the requirements of the Act of Uniformity and who was therefore in concert with the established Church of England, as opposed to those of the Nonconformists, whose practices were not acceptable to the Church of England.

Adjective

1. 1
   Conforming to established customs, etc.