It looks like your sentence was cut off. If you're trying to say that he is the only one among the students with a particular quality or in a specific situation, you would complete the sentence as follows:

- "He is the only one of the students who has completed the assignment."
- "He is the only one of the students who has won an award."

If you provide more context or finish the thought, I can help tailor the sentence more precisely to what you're trying to express.