Step 1: About Buddhist logic.
Buddhist logic (Hetuvidyā) developed strongly in the works of scholars like Dignāga and Dharmakīrti.
Step 2: Dharmakīrti’s role.
Dharmakīrti (7th century CE) is regarded as one of the greatest Buddhist logicians, who refined epistemology and logic.
Step 3: Analysis of options.
- Buddhaghoṣa: Famous commentator, not logician.
- Aśvaghoṣa: Poet and dramatist, author of Buddhacarita.
- Dharmakīrti: Correct, key Buddhist logician.
- Vasubandhu: Philosopher, but not primarily known as logician.
Step 4: Conclusion.
Thus, the Buddhist logician is Dharmakīrti.