Because power corrupts, society’s demands for moral authority and character increase as the importance of the position increases.

John Adams (1735–1826) American lawyer, Founder, statesman; US President (1797–1801)

(Misattributed)

This quotation is widely attributed to Adams online, but cannot be found in his written works. However, all the book references I can find to this quote and the attribution from Adams are from 2000 and later.

In addition, Anthony Hartle (at the time a US Army Colonel, and Vice Dean and English Department Head at West Point) wrote a book in 1989, Moral Issues in Military Decision Making. In chapter 2 of that book (and in the 2004 revised edition), in a discussion about the obligation to act honorably, he writes the above statement, not as a quotation, then in the next sentence mentions John Adams and provides a footnoted quote from him on a similar theme (but not with any of this quote's wording).

My judgment is that someone, reading Hartle's book, erroneously connected this phrase to Adams as well, from which it spread to a number of online quote resources and was thus treated as accurate. I believe the credit for the statement should go to Hartle.