The chairman of the World Superman Federation.
The World Supermen Federation (世界超人同盟 Sekai Chōjin Dōmei) (WSF) Chairman and pupil of God Von Erich. A parody of Ed "The Sheik" Farhat. An kaiju also named Shiek Seijin appeared earlier; it's not clear if they are the same person or not. In the anime he is depicted as Edith Harrison's minion.
Sheik Seijin first appears on a large screen, alongside his fighter Skull Bozu and the World Superman Council chairman: Edith Harrison.  He announces that he has joined forces with Edith to defeat Kinnikuman, but the two argue about who will fight against Kinnikuman first. They then leave the screen in anticipation of the fights. 
Later, during Kinnikuman's exploits and defeats of WSC and WSF members, Sheik Seijin begins to suspect that there is a conspiracy at play, perhaps caused by the World Superman Association.  He later realises that Channelman is Kinnikuman, working for the WSC, and that his suspicions were correct.  He fakes that he believes Channelman is not Kinnikuman, in order to later expose him in a public manner.  He then imprisons Kinnikuman while they wait for a match to take place between him and Robin Mask. 
After Robin Mask is defeated, the WSF assumes the championship belt, but Kinnikuman and Edith Harrison state that his side have not rightfully earned the belt.  God Von Erich appears to declare a tag tournament shall take place to determine its rightful owner.  Sheik Seijin is mostly seen in the background, as he helps his team and directs them from the stands or during training.  He is not seen again once The Machineguns defeat his team and unify the three American organisations.