Union territories are administered by the President. The President appoints an administrator as they see fit. Administrators include Lieutenant Governors or State Governors.

National Portal of India (Archive)

When the Indian Constitution was adopted in 1949, there was only one union territory: Andaman and Nicobar Islands.The National Capital Territory of Delhi, Chandigarh and Lakshadweep were formed by separating the territory from pre-existing states. Dadra Nagar Haveli, Daman Diu and Pondicherry were formed from acquired territories that formerly belonged to Portuguese India or French India.

Source: World Digital Library