Final answer:
Option (1), Charlemagne was the ruler who strengthened the influence of knights in Europe through his conquests and cultural initiatives such as the Carolingian Renaissance.
Step-by-step explanation:
The individual who strengthened the influence of the knights in Europe was Charlemagne. Serving as the most influential ruler in the early European Middle Ages, Charlemagne reorganized government, attempted to revive learning, and extended his influence far beyond his realm.
His campaigns and conquests throughout central Europe brought about the concept of the Holy Roman Empire and united western Europe for the first time since the Roman authority collapsed. Through the Carolingian Renaissance, Charlemagne also fostered a "rebirth" of culture and learning, thereby making his court a hub for educated advisors. This, in turn, reinforced the feudal system in which knights played a central role.