Final answer:
Pope Gregory claimed the pope was supreme over the church and state by creating beneficial relationships with kings and asserting authority using the forged Donation of Constantine document.
Step-by-step explanation:
Pope Gregory played a significant role in asserting the supremacy of the papacy over both the church and state. Alongside other popes, he strategically cultivated beneficial relationships with kings, gradually consolidating the authority of the papal office. This consolidation was further facilitated by overseeing the expansion of Christian missionary work, strengthening the influence of the church. In the eighth century, the papacy went as far as producing the Donation of Constantine, a forged document often cited as evidence of the pope's authority, solidifying their claim to supremacy.
However, the power of even influential popes had its limits, as political turmoil often led to their deposition or even death. Despite their efforts to centralize authority, the intricate dynamics of medieval politics and the challenges of maintaining control over vast territories meant that the authority of popes could be contested and constrained in various historical contexts.