From the following four alternatives, choose the one that can be substituted for the given words/sentence.

"One who is indifferent to pain or pleasure."

The words provided in the options and their meanings are listed below:

1. Eccentric: Someone who is (or whose behaviour is) bizarre, unconventional or strange.
2. Philosopher: Someone who studies philosophy or is concerned with thinking about the nature of things.
3. Fatalist: Someone who believes in determinism and fate.
4. Stoic: Someone who endures pain and hardship without complaining and showing emotions.

Out of the given options, only option D, 'stoic', alludes to "One who is indifferent to pain or pleasure," and is the correct answer.