As Yoda would say there can only be 2 siths; a Master and a apprentice but we cannot be sure of who really started the whole saga in Star Wars; we need to examine one individual that ties the strings from both videos and that individual would be Palaptine. At the beginning of this individual; he was Senator on Curosant he supervised everything but he did not grasp politics or power during the invasion of Naboo, he also hides in the mean time whenever he does not have anything to work on as a dark lord so the Jedi cannot discover him; since he controls the dark side under mysterious circumstances; in a way the Jedi thought the Sith was extinct at the time of the invasion; under mystery he has been working with the people responsible for the invasion the Trade Federation; he has the power to twist the invasion to a war that could last forever. He also had a apprentice that has a strong connection to the dark side that will continue into other individuals into the future. In the beginning Senator Palaptine persuaded the Queen of Naboo to vote for a new chancellor to bring back power to the senate. The vote choose him to be the next Chancellor which it could change him forever. He send his apprentice to distinguish the first 2 Jedi Obi Wan & Qui Gon; as it turns out the tide turned and his apprentice was immediately killed in a lightsaber duel but before he died; he send Obi Wan's master to the force. Palapatine knew it was no fair loss; he began to extend his interest in young Anakin Skywalker after that.
In the second movie Palapatine was Chancellor he now controls the senate with a iron fist; his first act as Chancellor he put motion to vote to create a grand army of the republic to fight against the Separatist movement. The vote went into motion and his army were actually clones for him to control during the Clone Wars. He became a father figure to Anakin which made Obi Wan suspicious as well as the Jedi. Every time he needed help; he would talk to Anakin alone, he even put seeds in young Skywalker telling him that he is more powerful than the Jedi; in a way he is playing with Anakin's emotions even his dark emotions that could change his destiny for years to come. Palpaltine's second apprentice was Count Dooku under dark scruntiny this time the Jedi noticed the dark side was within the Chancellor; with his time in the senate he gained more power than any other individual that could significantly change as the Clone Wars progress. Anakin & Obi Wan eventually fought Count Dooku during the War but he escaped to live another day.
As the Clone Wars progressed; the dark side contniued to grow stronger in Palpaltine; he persuaded Anakin to join the dark side; now we find out that it was palpaltine that started the whole thing; he has more power since has control over the Senate and the courts; he choose Anakin to be his next apprentice as Lord Vader, he started the whole war to gain more power; now he became corrupted with the darkside. His force lightning disfigured his body & mind. He planted more dark thoughts inside Anakin to betray his old master and to turn his back to the Jedi. He send Lord Vader to slay the last remains of the jedi inside the temple. Palpaltine made him to become Darth Vader the dark lord of the sith.
We don't see much of palpaltine in the New Hope; he eventually reappeared in the Empire Strikes Back in a hologram projection. He warned his apprentice of Vader's son that could become a jedi just like his father was, they both plan to send his son to the darkside which did not work at all. Within the last movie; Palpaltine became the evil Emperor. He persuaded to Luke that the darkside was the ultimate power to save his friend's lives. Luke knew that was a lie, he had saw what became of his father becasue of him, if it weren't for the Emperor Anakin would have been alive. Luke could sense inside that Anakin is still alive. The Emperor said it's too late for him. That made a tipping point inside Luke that cause him to fight his father one last time. The Emperor was delighted at the outcome, when Luke denouce the darkness; he became enraged and assaulted him with the same force lightning that caused Palpaltine to become his evil self. Vader made a huge mistake of having to keep his master alive; so threw him down the core shalft causing him to explode and die.
