Qutbuddin Mubarak Khalji referred to himself as the Caliph among the given Sultans of Delhi. Here is an explanation of this answer:

Introduction:
The Caliph is the title given to the political and religious successor to the Islamic prophet Muhammad. It signifies the leader of the entire Muslim community and holds great significance in the Islamic world.

Explanation:
Among the given options, Qutbuddin Mubarak Khalji regarded himself as the Caliph. Let's understand the reasons behind this:

Establishment of the Khalji Dynasty:
- Qutbuddin Mubarak Khalji was a prominent figure in the Khalji dynasty, which ruled the Delhi Sultanate from 1290 to 1320.
- He was the founder of the dynasty after overthrowing the last ruler of the Slave dynasty, Jalaluddin Firuz Khalji, in 1290.
- Qutbuddin Mubarak Khalji took over as the Sultan of Delhi and proclaimed himself as the Caliph, signifying his authority as both the political and religious leader.

Religious Justification:
- Qutbuddin Mubarak Khalji justified his claim of being the Caliph based on his religious beliefs.
- As the Caliph, he aimed to establish his authority not only as a ruler but also as the supreme leader of the Muslim community in India.
- This title gave him the legitimacy to exert control over religious matters and establish Islamic law (Sharia) throughout his kingdom.

Political Implications:
- By assuming the title of Caliph, Qutbuddin Mubarak Khalji aimed to consolidate his power and gain the support of the Muslim population.
- The title held immense religious significance and commanded respect from the believers.
- It also helped him to assert his authority over other Muslim rulers in the region, portraying himself as the rightful successor to the Prophet Muhammad.

Conclusion:
Qutbuddin Mubarak Khalji, the founder of the Khalji dynasty, regarded himself as the Caliph. This title not only gave him religious authority but also helped him consolidate his power and establish his legitimacy as the ruler of the Delhi Sultanate.