Great Leader of Shocker

"Takeshi Hongo, welcome... to Shocker!"

- The Great Leader of Shocker's first words spoken to Takeshi The Great Leader of Shocker is the primary antagonist of the original 1971 Kamen Rider series, as well as the Showa continuity of Kamen Rider as a whole. He is a mysterious entity who is force behind nearly every evil organization the Kamen Riders have faced. His ultimate goal is to conquer the world and convert the entire human race into kaijin, uniting the world as one being.

Following his original defeat, later incarnations of him would go on to serve as the main antagonists of several other Showa Kamen Rider series. He eventually returns as the main antagonist of the crossover film, Let's Go Kamen Riders and the main antagonist of the film Super Hero Taisen GP: Kamen Rider 3.

He was voiced by the late Gorō Naya in most of his appearance and incarnations.

Physical Appearance
The Great Leader wears a red robe with a KKK-esque hood and a medallion with the Shocker logo in the center. Under his hood are Medusa-like snakes that cover his true cyclops head.

Kamen Rider
He initially issued orders to his subordinates via speakers on Shocker's bases. After the two Kamen Riders, Hongo and Ichimonji, eliminated Colonel Zol, Doctor Shinigami and Ambassador Hell, several of Shocker's important members, the Great Leader allyed with General Black of Geldam and merged the two organizations to create Gel-Shocker. Believing that the old members of Shocker were unfit for Gel-Shocker, the Great Leader had them executed, with Shocker's secret bases being self-destructed and the remaining Shocker soldiers killed. The Double Riders defeated Gel-Shocker's, including General Black, and located Gel-Shocker's headquarters, finally confronting the Great Leader himself. The two riders pulled off the Great Leader's hood revealing his snake mask. Pulling that off revealed his true Cycloptic face. The Great Leader set off the headquarters' self-destruct system hoping to kill the Kamen Riders, but the two riders were able to escape, leaving him to be killed as the base exploded and finally destroying Shocker. This was not the end of the Great Leader however.

Remergences
Shortly after, the Great Leader resurfaced as the Great Leader of Destron. In response, the Double Riders creating the third Kamen Rider, V3. The Great Leader founded more terrorist organizations to conquer the world, but this only resulted in the creation of more Kamen Riders.

His last incarnation to appear in the Showa series was the Generalissimo of the Badan Empire, who made appeared to the ten veteran Kamen Riders after Ambassador Darkness's death.

The Great Leader may have also been the Grand Lord Crisis of the Crisis Empire, as they share the same voice ac

OOO, Den-O, All Riders: Let's Go Kamen Riders
The Great Leader makes a return in the movie OOO, Den-O, All Riders: Let's Go Kamen Riders, serving as the film's main antagonist. During a small conflict between the characters of Kamen Riders OOO and Den-O during their time travel in Japan during the 1970s while hunting the Imagins, General Black discovered a Cell Medal that was accidentally dropped by Ankh during the conflict and gave it to the Great Leader. The Great Leader combined it with the Shocker medal, creating Shocker's most powerful kaijin, Shocker Greeed. Shocker Greeed later defeated both Hongo and Ichimonji, allowing Shocker to create an alternate timeline where the conquered the world. Various evil organizations that had existed in the normal timeline were annexed into Shocker, with their highest members serving as part of Shocker's high council. Shocker also brainwashed Hongo and Ichimonji to become members of the organization.

OOO and Den-O returned to 1970s Japan in hopes of stopping Shocker Greeed from being created and returning the timeline back to normal. The Great Leader was confronted by the Riders, but was able to create Shocker Greeed and the kaijin manage to take down the Riders. Having failed to restore the timeline and the DenLiner destroyed, the Riders retreated back to the Shocker-ruled future and decided to confront Shocker, but were overwhelmed by the various kaijin forces. As the Riders were about to be publically executed, Hongo and Ichimonji (having been faking their brainwashing in order to wait for the right time to fight Shocker) summoned all the other Riders and were able to defeat the kaijin army.

The Double Riders have a rematch with Shocker Greeed while the other Riders rushed toward Great Leader. Shocker Greeed is destroyed by the Rider Double Kick before Ankh takes the Shocker Medal. When the Riders are overpowered by Great Leader's attacks, Ankh convinces OOO to use the Shocker Medal and an Imagin Medal from Momotaros in combination with the Taka Medal. With the three Medals, OOO changes into Tamashii Combo and destroys Great Leader with the Tamashii Bomber. The attack, however, unleashes Great Leader Colossus - the true form of Great Leader, who throws fireballs at the Riders and consumes the other Shocker leaders in an earthquake. The Riders are joined by Kamen Rider Birth and all of the extra Riders to battle the new menace. All of the Riders jump into their motorcycles to execute the All Rider Break, destroying Great Leader Colossus once and for all.

Super Hero Taisen GP: Kamen Rider 3
However, the Great Leader's spirit managed to survive and possessed the History-Modifying Machine, using it to send Kamen Rider 3 back in time to defeat the Double Riders, allowing Shocker to achieve its domination of the world. He later absorbed Kamen Rider 3 into the machine to power it, shifting it into the Rider Robo to destroy the Kamen Riders. He was finally destroyed when Kamen Rider Drive's Tridoron combined with the Ninningers' mech Shurikenjin and they used their combined power to defeat him.

Kamen Rider Decade
For the more information on the Great Leader's Decade Incarnation, see here

In the Heisei period film Kamen Rider Decade: All Riders vs. Dai-Shocker, Tsukasa Kadoya (Kamen Rider Decade) was the Great Leader of Dai-Shocker, before he was overthrown by Shadow Moon. Tsukasa later became Great Leader again during the events of Kamen Rider × Super Sentai: Super Hero Taisen, before revealing that he was actually working to sabotage Dai-Shocker's Big Machine operation.

Powers and Abilities
Great Leader's primary ability is summoning gas from his body to knock out his foes. and whilst he never did this in the original series, in the Let's Go, Kamen Rider movie, he could use the snake heads as tendrils coming from his head and shoot fireballs from ths snake's mouths.

Also in that film, he became his greatest form, the Great Rock Leader, one of the largest entities in both Kamen Rider and Super Sentai (one of the closest is Black Cross Fuhrer).

The Great Leader is also seemingly unkillable, as any time he is defeated or destroyed, he returns in a new form or resurfaces to antagonize the Riders regardless if he was defeated before. (Usually by time travel or distortions in space/time)

Trivia

 * The Great Leader bears some similarities to Demise as both have more than one incarnation and are known to be "hijacking the story" though the former has more incarnations than the later.
 * The Great Leader's seemingly immortal presence has vaguely been explained and has multiple variations:
 * Kamen Rider co-creator Toru Hirayama stated in an interview in the Uchûsen Book Collection Special Edition that the Great Leader was once a monk named Chan Mao who discovered the secret of transcending death. This led him to be detached from humanity and eventually drove him to lose his own, as he became an evil demigod-like figure who wanted to rule the world.
 * The series Kamen Rider Stronger contradicted this by showing that the Great Leader was in fact an alien cycloptic brain. This was again contradicted when it was revealed in Skyrider that the Great Leader was a giant dragon.
 * In the Manga Kamen Rider Spirits, he is called JUDO and is an Eldricth Monster who seeks to inhabit a vessel in the form of a cyborg human body.
 * The last explanation is a speculative one by fans based on a line from Kamen Rider Black RX, "As long as Humanity's evil exists, there will be a new Crisis Empire! And I will return to lead it!". This could mean that the Great Leader somehow uses the human race's own evil and hatred to sustain and regenerate himself.