Bottom line, Dooku never considered himself a Sith. And he wasn't; he was a man looking to change the galaxy in a way the Jedi were unwilling to try. And that is why he joined the Sith and became Darth Sidious' apprentice, Darth Tyrannus. When Dooku became Sidious's apprentice, he was already an elderly man.
The reason Dooku joined the Separatists, he said, was that he learned a terrible truth: a Sith Lord called Darth Sidious controlled the Senate. With Obi-Wan at his side, they could destroy the Sith. “I'll never join you, Dooku,” the Jedi said.
Technically Dooku is a Darth as well, as the Emperor renamed him Darth Tyranus when he became his apprentice in Attack of the Clones, yet in a universe where Jedi and Sith usually claim similar titles like "Master" or "Darth," Dooku is a Count. This topic of Dooku's interesting title was discussed on Quora.
Like many of the other Sith, Count Dooku was incredibly proficient with the Force, even being able to win a fight against Yoda. Despite this, though, he still wasn't the best fighter with a lightsaber, and his Force skills were not nearly as powerful as Darth Vader's.
A former Jedi Master, Dooku had lost faith in the Republic and in the Jedi, believing them to be too tied to a corrupt political institution. He left the Jedi and fell under the sway of Darth Sidious, apprenticing to him in the hopes of bringing peace and order to the galaxy.
Anakin regrets this decision, and Palpatine reasons with him saying that Dooku was too dangerous.
Though he saw Anakin's potential, Yoda could not ignore the danger inherent in Anakin's unrestrained emotional attachments. To teach Anakin responsibility, Yoda assigned Skywalker a Padawan learner: Ahsoka Tano. Yoda knew there would come a time when Anakin had to let go of Ahsoka.
1 Darth Sidious
There has been no Sith, as powerful, meticulous, nor as evil as the Emperor himself, Darth Sidious. As previously mentioned, Sidious trained in the Dark Side by Darth Plagueis before Sidious killed Plagueis in his sleep, making Sidious a Sith Master.
Revenge of the Sith (2005)
Anakin gives in to his hatred of Dooku and uses his anger to overpower him, severing both of Dooku's hands and leaving him helpless.
In legends, Dooku actually explains why he hates Anakin: He could feel Yoda's touch still lingering on the edges like a distant echo. Vividly his mind went back to their last meeting, on Geonosis: swords drawn at last, and finally equal.
Vader's own grandson, Ben Solo/Kylo Ren, would follow in his grandfather's dark side footsteps to make the dark side supreme. However, Kylo Ren never took on the name of Darth, even though he worshipped everything about the Sith that came before him.
Studying Jedi Archive records, Dooku based his new weapon design after the curved hilts that were standard during the heyday of Form II lightsaber combat. The curve allowed the hilt to fit better into his hand, allowing for superior finesse and precise blade control.
In the now-abandoned Legends continuity, his birth name appeared to be Maul, with the title of "Darth" simply added to it when he was taken on as an apprentice by Darth Sidious.
Obi-Wan Kenobi
Obi-Wan was Dooku's polar opposite. Dooku hoped to have Obi-Wan as his Sith apprentice and went as far as to reveal Sidious's existence to convince him to join him. Obi-Wan didn't believe him and refused, resulting in the two being enemies ever since.
Palpatine knew that the only way for Anakin to defeat Dooku was by tapping into the dark side of the Force. If Anakin did this he would surpass Dooku and carry out the rule of two, also Dooku was much older than his master Palpatine and didn't have the potential to defeat him and become the Sith master but Anankin did.
When Dooku left the Jedi Order to become a Sith Lord, Yoda thought he merely left rather than turned to the Dark Side. Dark side clouded jedi orders ability to sense things properly. Also yoda did not believe dooku was a Sith lord.
In one of the canon comics Sidious outright implied that Maul was pretty much head and shoulders above Dooku when adressing the potential. While Dooku was a useful pawn for him, Maul in the other hand seems to be actually his first choice as a heir before Anakin was really part of the picture at least.
Count Dooku Plotted Against Palpatine With Ventress
As revealed in Star Wars: The Clone Wars, Dooku trained Asajj Ventress as his unofficial Sith assassin not only to have a deadly Separatist agent at his disposal but as a true Sith Apprentice to help him overthrow Palpatine and take his place as the Sith Master.
Master Yoda has risen above all others to claim the top spot as the most powerful Jedi of all time and the true chosen one according to IGN's audience. He won pretty handily as well, as he was victorious in 89,756 of his 95,243 battles and had a win percentage of 94.2%.
killed by an Imperial strike team, his dark side, like many Seth before him, refused to let go of life.
Mission to Mathas. Padawan Windu was trained in the ways of the Force by Jedi Master Cyslin Myr. Following his early trials as a youngling, Windu attained the status of Padawan by becoming Jedi Master Cyslin Myr's apprentice.
Billaba became Windu's Padawan and trained under the Jedi Master in the ways of the Force. During her training, Windu allowed her to study Form VII variant known as Vaapad. She eventually became a Jedi Knight, renowned for her skills with a lightsaber and favored Form III when teaching other Jedi.