Explanation:

The Delhi Sultanate was a Muslim dynasty that ruled over the Indian subcontinent between the 13th and 16th centuries. During this period, several cities were established and developed by the Sultanate rulers. These cities served as important administrative, commercial, and cultural centers of the Sultanate.

The cities developed by the Delhi Sultanate are as follows:

Siri:
- Siri was the first city established by the Delhi Sultanate in 1193.
- It was established by Qutb-ud-din Aibak, the founder of the Slave Dynasty.
- Siri served as the capital of the Delhi Sultanate from 1193 to 1206.

Jahanpanah:
- Jahanpanah was established by the Sultan Muhammad bin Tughlaq in 1326.
- It was built to accommodate the growing population of Delhi.
- Jahanpanah was fortified with walls and served as a refuge for the people of Delhi in times of war.

Delhi-i-Kunha:
- Delhi-i-Kunha, also known as Old Delhi, was founded by the Sultan Sher Shah Suri in 1540.
- It was built on the site of the ancient city of Indraprastha, which was mentioned in the Mahabharata.
- Delhi-i-Kunha served as the capital of the Sur dynasty and later the Mughal Empire.

Agra:
- Agra was not developed by the Delhi Sultanate.
- It was founded by the Rajput ruler Raja Badal Singh in the 11th century.
- Agra came under the control of the Delhi Sultanate in the 12th century, but it was not developed by the Sultanate rulers.

Conclusion:
In conclusion, the city that was not developed by the Delhi Sultanate is Agra. The other three cities, Siri, Jahanpanah, and Delhi-i-Kunha, were established and developed by the Sultanate rulers and played important roles in the history of the Delhi Sultanate.