We use the superlative to compare somebody/something with the whole group that she/he/it belongs to.
- Tom is the tallest of the four brothers.
- Gold is the most precious of all metals. (OR Gold is the most precious metal.)
Nouns with superlative adjectives normally take the article the (unless there is a possessive).
- She is the best girl in the class. (NOT She is best girl …)
Superlative adjectives in predicative position also tend to take the, though it is sometimes dropped in an informal style.
- This book is (the) best.
The is sometimes dropped before superlative adverbs in an informal style.
- Who can run (the) fastest?
After superlatives, we do not usually use of with a singular word referring to a place or a group.
- He is the richest man in the world. (NOT … of the world.)
- Who is the fastest player in the team? (NOT … of the team?)
But of can be used before plurals, and before singular quantifiers like lot and bunch.
- Iron is the most useful of all metals.
- He is the best of the lot.