The Gurjara Pratihara Dynasty was founded by:

Historians identify the founder of an early medieval Indian dynasty from epigraphic and numismatic evidence — inscriptions, coins, and dynastic genealogies (prashastis) recorded by later rulers of the same line — which name the ancestor who first established independent political authority, as distinct from earlier feudatories or later rulers who only expanded or restored the kingdom.

Applying this to the Gurjara-Pratihara dynasty: dynastic inscriptions and later prashastis credit Nagabhatta I (ruling roughly 730-760 CE) with establishing independent Pratihara power in the Malwa-Rajasthan region and with repelling an Arab expedition that had advanced from Sindh into western India - the marker historians treat as the founding of the dynasty as an independent power, distinct from any earlier feudatory status.

• Gopala founded a different, contemporary dynasty - the Pala dynasty of Bengal - not the Gurjara-Pratihara dynasty.

• Mihira Bhoja (Bhoja I) was a later Gurjara-Pratihara ruler who expanded the kingdom to its territorial peak in the 9th century, generations after the dynasty was founded.

• Krishna I belonged to a different dynasty altogether — the Rashtrakuta dynasty of the Deccan, founded earlier by Dantidurga — and is remembered for commissioning the rock-cut Kailasa temple at Ellora, not for founding any dynasty.

Hence, the Gurjara-Pratihara dynasty was founded by Nagabhatta I.