A person such as Tyra Banks could be said to be a champion, advocate, proponent, or promoter of "diversity in beauty ideals and self acceptance".
champion: a person
who fights for or defends any person or cause
advocate: a person
who speaks or writes in support or defense of a person, cause, etc.
proponent: a person
who argues in favor of something; an advocate.
promoter: a person or
thing that promotes, furthers, or encourages.
A person who uses their career to benefit humanity and/or the environment in some way could be said to be a humanitarian (as noted by @SteveSliva) or an environmentalist.
a person actively engaged in promoting human welfare and social
reforms, as a philanthropist
any person who advocates or works to protect the air, water, animals,
plants, and other natural resources from pollution or its effects