- You may be looking for the Robot Knight created by Sontaran Jingo Linx.
A group of robots who masqueraded as a force of medieval knights travelled aboard a spaceship, observed by the Twelfth Doctor to have come from the 29th century, which had crash landed on Earth in the past while on a destination to the Promised Land.
The ship surfaced as the castle of Nottingham in 12th century England. By this point, they served the Sheriff of Nottingham, who aspired to take the English throne. Most were destroyed by the Twelfth Doctor, Maid Marian and a peasant uprising, but at least two survived to flee in their ship. Knowing the ship was too damaged to make it to orbit, the Doctor, Robin Hood and Clara Oswald fired a golden arrow into the ship's engine, giving it enough of a boost to reach orbit where it exploded harmlessly, destroying the last of the robots. (TV: Robot of Sherwood)
The robots could pass themselves off as ordinary knights, wearing armour, chainmail and tunics that were customary of the Medieval era.
They were quite proficient with swords and displayed considerable skills at swordsmanship.
For armaments, the robots were equipped with a powerful laser concealed in their head that was fired out of their face. It gave off a purple glow. It was powerful enough to cause a large explosion the size of a grenade blast, but at full power, it could completely disintegrate a human being, leaving nothing behind but a charred pile of ash. (TV: Robot of Sherwood)