Obi-Wan Kenobi used Form III.
Throughout his career as a Jedi knight, Obi-Wan used Form III Soresu in lightsaber combat, which was originally created as a counter to the dueling intricacies of Form II's fencing style and focused on minimizing movements while optimizing defense.
Obi-Wan Kenobi was highly skilled in Form III. Over the course of the Clone Wars, Kenobi continued to develop his skills.
Obi-Wan originally used Form IV commonly known as Ataru like his master, Qui-Gon Jinn. After Qui-Gon's death, Obi-Wan realized the flaws of Form IV and instead became a practitioner of Form III, Soresu, which is the most defensive of the seven lightsaber forms.
I noticed in the finale when Kenobi was fighting Vader he was more aggressive and acrobatic. It seems he switched to Form IV, the same form favoured by Yoda, Qui-Gon and Ahsoka. Kenobi is known to be a great master of Form III.
Notable users of this combat form during the Old Republic included Yoda and Qui-Gon Jinn. The New Jedi Order preserved knowledge of Ataru, and Jedi Masters such as Luke Skywalker, Mara Jade Skywalker, and Kyle Katarn all employed it.
Kylo Ren's lightsaber form was something of a hybrid, which blended three styles together: Djem So, Juyo, and Niman. Djem So used an irregular reverse grip and was meant for practitioners who loved fighting with a more offensive edge - a perfect fit for Ren.
Darth Sidious was also one of the greatest and most skilled Sith swordmasters, as he has mastered all the seven lightsaber forms, all their stances and techniques and is capable of using each form equally effective ambidextrously.
Form VII, known by its two primary disciplines of Juyo and Vaapad; and also known as The Ferocity Form, was the seventh form of lightsaber combat. It was considered the most aggressive and unpredictable form.
Form VI, also known as Niman, was the sixth form of lightsaber combat used by members of the Jedi Order.
The Third Sister is later involved in trying to track down Obi-Wan Kenobi, an Order 66 survivor, whom she specifically targets out of a desire to gain Darth Vader's favor, all just to get closer to Vader and kill him for killing her youngling friends long ago.
At first, Rey primarily fights with a lightsaber the same way she would have with her quarterstaff. However, after studying Luke's Jedi scripture and training with Leia, Rey probably uses Form VI: Niman, a jack-of-all-trades lightsaber form that combines different aspects of Forms I through V.
Vaapad. Mace Windu was known among the Jedi Order for his use of Vaapad, a variation of Form VII.
Sokan was a form of lightsaber combat. Developed by the ancient Jedi Knights during the Great Sith War, Sokan combined tactics that allowed for evasion and mobility with the kinetic motions of Form V combat.
The Third Sister was at the Jedi Temple during Order 66. She either saw Anakin kill her fellow Jedi or saw the recording of his crimes. That's why she has such hatred for Obi-Wan. She was a Padawan who escaped Order 66.
Vader's son, Luke Skywalker, learned Form V in part by mirroring the swordplay of his father in their first duel, and the younger Skywalker ultimately defeated his father with his use of Form V during their second duel.
Form Zero was a principle followed by many Jedi, not exactly a form of lightsaber combat despite its name. The principle of Form Zero was that a Jedi's most important martial skill was to know to only draw one's lightsaber when absolutely necessary.
A Form I specialist who lived during the Clone Wars was Kit Fisto, who was credited as one of the best duelists in the Jedi Order. His mastery of the form was advanced, and he applied it in many battles and duels, always with his trademark smile.
Form IX: Kadeesh was a Form of lightsaber combat mainly focusing on the use of brute strength rather than Force-assisted movements or fancy and unpredictable parries.
Form I, also known as Shii-Cho, The Way of the Sarlacc, or The Determination Form, was the oldest and most rudimentary form of lightsaber combat developed by the Jedi Order and was taught to all members of the Jedi Order.
In fact, Yoda was trained in all seven forms of lightsaber combat and had full mastery and knowledge of all of them. He was considered to be the best instructor at the Jedi Temple when it came to lightsaber combat, knowing which forms were most appropriate for each of his students.
You may be looking for Gormo, the Duros captain of Tweigar. N'Kata Del Gormo was a Force-sensitive male Hysalrian Jedi Master who lived during the times of the Galactic Republic. According to legend, he found and trained Yoda and a Force-sensitive Human friend.
Anakin used the form 5, it's known a the Way of The Krayt Dragon. Form 5, also known by its two primary disciplines of Shien and Djem So, is the offensive version of form 3 and relies on strength.
For Ahsoka, lightsaber form is crucial because she's a dual wielder. While Jar'Kai is the method of dual wielding, Ahsoka Tano's lightsaber form is a variant of Form V, much like her master, Anakin Skywalker.
Kyber crystals are rare gems that possess a natural connection to the force. Kyber crystals have to be mined from deep within the ground, and so they are only found on specific worlds like Ilum, Exegol, Jedha, Lothal, and Utapau among others.