An old man lived in the village. He was one of the (1) ______ unfortunate people in the world. The whole village was tired (2) ______ him; he was always gloomy, he (3) ______ complained and was always in a bad mood. The (4) ______ he lived, the more vile he was becoming and the more (5) ______ were his words.

Select the most appropriate option to fill in blank number 4.

The correct option to fill in blank number 4 is longer.

Explanation:
The sentence structure here is a double comparative, which is used to show a parallel increase or decrease between two situations (i.e., "The [comparative degree], the [comparative degree]").
In the given sentence, the structure is: "The (4) ______ he lived, the more vile he was becoming..."
Since "more vile" is in the comparative degree, the word filling blank (4) must also be in the comparative degree to maintain grammatical symmetry.

Let us evaluate the options:
1. long - This is the base (positive) adjective and does not fit the comparative construction.
2. lengthy - This is an adjective meaning very long, which does not fit the grammatical requirement.
3. longer - This is the comparative form of "long" and correctly completes the pattern "The longer..., the more...".
4. longest - This is the superlative form and is incorrect in a double comparative structure.

Thus, longer is the grammatically correct choice.