The Knights of the Round Table (円卓の騎士, Entaku no Kishi) are the protectors of Camelot under King Arthur. Called such for having gathered around the Round Table as equals with each other and their King, they were admired throughout the country.
Every single knight who sat on that table was a hero sung of in legends, and any of them would boast indisputable fame and strength if summoned as a Servant. Their overall numbers vary depending upon the story, but the world of Fate/stay night accepts the standard pattern of thirteen knights.
I can play any of the knights of the round table, be it at the time they were alive, during the Camelot singularity or even as just normal servants, feel free to ask!
(Male writer, but am currently writing as both male and female characters)