Another use for the preposition of is in showing leaders
of various types of organizations or groups:

the Archbishop of Canterbury

the board of directors

the captain of a ship

the chair(person) of the ways and meanscommittee

the Chief Justice of the Supreme Court

the conductor of an orchestra

the director of the finance department

the executive secretary of a corporation

the first vice president of a company

the Governor of Texas

the headmaster of a school

a member of the board of directors

the Minister of Education

the President of the United States

the Prime Minister of Canada

a representative of an organization

the Secretary General of the United Nations

the Speaker of the U.S. House of Representatives

a vice president of a corporation

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Of is also frequently used after superlatives:

the angriest of the protestors

the best of luck

the most casual of friendships

the most difficult of the questions

the easiest of the jobs

the fondest of my memories

the greatest of her difficulties

the highest of the mountains

the most just of causes

the latest of the arrivals

the most marvelous of experiences

the noisiest of the children

the most offensive of remarks

the most painful of his experiences

the most revealing of his statements

Note the difference in meanings:

the angriest of the protestors is not the same as
the angriest protestors (instead, it means 'the one
protestor who is angrier than any other')

the most casual of friendships is not the same as
the most casual friendships (instead, it means 'the one
friendship that is more casual than any other')

the most difficult of the questions is is not the same as
the most difficult questions (instead, it means 'the one
question that is more difficult than any other')

etc.

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Next: more ways to use of