Definition of "guardian"

Thoſe who ought to be the guardians of propriety are often the perverters of it. Hence Accidence for Accidents, Prepoſtor for Prepoſitor and Conſtur for Conſtrue […]

1791, John Walker, A Critical Pronouncing Dictionary […] ‎, London: Sold by G. G. J. and J. Robinſon, Paternoſter Row; and T. Cadell, in the Strand, page 162

As your Senior Tutor, I am your moral guardian,’ he said at last. ‘A moral guardian yearns for an immoral ward and the Lord has provided.

1991, Stephen Fry, The Liar, page 52:

Secret weak points of bosses/guardians.

1993, Zach Meston, J. Douglas Arnold, Awesome Super Nintendo Secrets 2

'if you tell me how to find the secret door in level three, I'll tell you how to defeat the end of level guardian'

2004, James Newman, Videogames