Guthrum was a formidable Danish Viking leader in 9th-century England, known as the primary adversary of Alfred the Great, a ruthless pagan sea-king who led invasions, conquered Anglo-Saxon kingdoms, but ultimately converted to Christianity after defeat at the Battle of Edington, becoming King of East Anglia under the name "Athelstan". He was a cunning warrior, a skilled administrator, and a significant figure who shaped England's political landscape, establishing the Danelaw before dying in 890.

Key Characteristics & Role:
Viking Leader: Led the Great Heathen Army and the Great Summer Army, invading and conquering large parts of England.
Fierce Warrior: Known for his military prowess, audacious attacks (like the surprise at Chippenham), and ambition to rule.
Adversary of Alfred: His prolonged struggle with Alfred the Great defined much of the Viking era in England.
Transformation: After his defeat, he famously converted to Christianity, became Alfred's godson, and ruled East Anglia as a Christian king (Athelstan).
King of East Anglia: Established a Danish kingdom, issued coins, and signed the Treaty of Wedmore, dividing England.

Physical & Personality (Inferred/Fictional): While historical descriptions focus on his actions, fictional portrayals (like The Last Kingdom) often depict him as a tall, imposing, battle-scarred warrior with a fierce demeanor, reflecting his pagan roots and ruthless ambition.

Legacy: His life marked a significant shift in Viking fortunes, from outright conquest to negotiated settlement, leading to the creation of the Danelaw. His baptism and reign as Athelstan symbolized a new era of coexistence between Vikings and Anglo-Saxons, notes The Oxford Reference.