One of the oldest German dynasties — dukes of Saxony and Bavaria, rivals of the Hohenstaufen, and, in Otto IV, the only Welf to wear the imperial crown.
The Welfs were an ancient Frankish-Swabian family who, by marriage and inheritance, gathered the duchies of Bavaria and later Saxony. Their name became a byword for a whole political tradition: in Italy the pro-papal "Guelph" party took its name from the Welfs, set against the "Ghibelline" supporters of the Hohenstaufen emperors.
The house reached its zenith under Henry the Lion, who ruled Saxony and Bavaria together, pushed German settlement eastward into Slavic lands, and founded cities including Munich and Lübeck.
Henry the Lion’s power rivalled that of the emperor himself, and his refusal to support his cousin Frederick Barbarossa in Italy led to his downfall: in 1180 he was stripped of his duchies, which were broken up, and driven into exile in England, where his marriage to a daughter of Henry II tied the Welfs to the Angevin kings.
The family kept its allodial lands around Brunswick, and from that base Henry’s sons contended again for the highest prizes of the Empire.
In the disputed succession after 1197 the Welf Otto IV was elected king against the Hohenstaufen Philip of Swabia, and after years of civil war he was crowned Holy Roman Emperor in 1209 by Pope Innocent III. The alliance soon broke: Otto invaded papal Italy, was excommunicated, and faced the young Hohenstaufen Frederick II, whom the pope now backed.
Otto’s bid collapsed at the Battle of Bouvines in 1214, where he fought alongside King John of England and was routed by Philip II of France. He lost the Empire to Frederick II and died in 1218. The Welfs endured as dukes of Brunswick-Lüneburg, and in 1714 a descendant became King George I of Great Britain as the House of Hanover.