The adjectives superior, inferior, senior, junior, prior, anterior and posterior take to instead of than.

• The death of King Edward VII was prior to World War I.
• He is senior to me.
• He thinks I am inferior to him in intelligence.

To compare two things or two groups of things, we use the comparative and not the superlative.

• Take the shorter of the two routes.
• He is the taller of the two.
• She is the prettier of the two sisters.

Notes
This rule is no longer strictly observed and many people use the superlative instead of the comparative.

• She is the prettiest of the two sisters.

The use of double comparatives and superlatives was once common in English.

• It was the most unkindest cut of all. (Shakespeare)

In modern English, double comparatives and superlatives are not used.

• Incorrect: The little town had never seen a more costlier wedding.
• Correct: The little town had never seen a costlier wedding.

Note
Lesser (a double comparative) is an exception to this rule. It is used even by the best authors.

The lesser of the two evils

Related posts:

1. Formation of the Comparative and the Superlative
2. Degrees of Comparison
3. Adjectives of Number (Numeral Adjectives)
4. Adjectives
5. Kinds of Adjectives
6. Demonstrative Adjectives
7. Interrogative Adjectives
8. Formation of Adjectives
9. Joining two sentences using adjectives