Step 1: Background.
The Fourth Buddhist Council (Mahāyāna tradition) was held in Kashmir in the 2nd century CE.
Step 2: Patron.
This council was convened under the patronage of the Kushan emperor Kaniṣka.
It led to the compilation and spread of Mahāyāna doctrines.
Step 3: Analysis of options.
- (1) Aśoka: Patron of the Third Buddhist Council, not the fourth.
- (2) Kalāśoka: Patron of the Second Buddhist Council.
- (3) Kaniṣka: Correct, patron of the Fourth Buddhist Council (Mahāyāna).
- (4) Ajātaśatru: Patron of the First Buddhist Council.
Step 4: Conclusion.
Hence, the patron of the Fourth Buddhist Council was **Kaniṣka**.