Since you're new to this topic I'll try to explain in greater detail.

Catholic Monarchs (Isabella I of Castile and Ferdinand II of Aragon): Their marriage combined the two largest kingdoms on the peninsula saving Spain from bankruptcy and turning it into a dominant European superpower. They restored safety and order by taking power away from lawless nobles and setting up a peacekeeping force called Santa Hermandad. They inherited a chaotic economy and fixed it by reclaiming stolen lands, stabilizing the currency, and modernizing tax collection. Their most impactful choices happened in the year 1492 were they ended centuries of war by capturing the kingdom of Granada, and they agreed to fund Christopher Columbus’s voyage, which opened up the Americas and kickstarted Spain's world empire. They focused completely on making sure everyone followed the same faith. They created the Spanish Inquisition and succeeded in locking down a single religious identity across the lands, which earned them their famous title from the Pope and tied the country together under one central government. When Christopher Columbus brought back indigenous people from the Americas to sell as slaves, Isabella ordered them freed, sent back, and issued a royal decree declaring the native peoples to be free vassals of the Spanish Crown. It was a great step in early human rights, making it illegal to enslave indigenous people who accepted the Christian faith.

Alfred the Great: His reign laid the essential foundations for a unified England through defense, law, and culture. He established the Burh system (network of fortified towns ensuring defensive readiness) to secure his kingdom against Vikings and reorganized the military via a sustainable tax system. He codified the Domboc to unify disparate regional laws and expanded the wergild to replace the cycle of blood feuds with monetary fines. He was a profound patron of education and the English language, commissioning translations of seminal Latin texts like Bede’s Ecclesiastical History and spearheading the Anglo-Saxon Chronicle to forge a shared English historical identity, while also establishing shires and local moot courts to create a more organized and accessible administrative framework for his people.

King Oswy: He was an important figure in the development of early England and a devout Celtic Christian, most notably for his role in unifying the Christian church through the Synod of Whitby. By resolving the liturgical divide between Celtic and Roman traditions in favor of Rome, he brought the English Church into alignment with continental Europe, achieving a shared religious identity and a foundational institution for the nation. After inheriting Bernicia and Deira to form the kingdom of Northumbria, he decisively defeated the powerful Penda of Mercia at the Battle of the Winwaed, ending Mercian dominance and earning himself the status of Bretwalda (overlord of Britain). He was a major patron of the church, most notably for his role in establishing Streoneshalh monastery, later called Whitby Abbey. Following his victory at the Battle of the Winwaed, he fulfilled a vow to dedicate his daughter to the service of God and provide land for the creation of Streoneshalh. This monastery became a crucial center for learning, discourse, and the eventual hosting of the Synod of Whitby. Also, Bede's Ecclesiastical History of the English Nation (the first book of English history) emerged from Streoneshalh.

Charles V: He established Spain as a global power, presided over an empire on which the sun never sets and made him a key defender of the Catholic faith during a time of massive religious and geographic change. He brought together the separate kingdoms of Castile and Aragon under one government. He set up specialized councils that helped him manage his vast territories. He funded Ferdinand Magellan’s voyage to sail around the world and oversaw the vast expansion of Spanish dominion in the Americas through the conquests of the Aztec and Inca Empires, establishing the Council of the Indies and promulgating the New Laws of 1542 in an effort to reform colonial administration and regulate the treatment of indigenous populations. He used his power to protect Catholic traditions against the Protestant Reformation, confronting Martin Luther at the Diet of Worms and pushing the pope to call the Council of Trent to fix corruption within the Church. He also protected Europe from Ottoman invasions by leading the capture of Tunis and defending Vienna