The mane is a breed of Khajiit that is very rare, and is an important figure in Khajiit culture. He used to be the reason Khajiit would shave off their manes. Cathay or Cathay-Raht are often seen carrying him around because his mane has made him unable to move due to it being so heavy. I don't know if he is still an important ruling figure, though. He might still be up there with the clan mothers.
Okay, so I can give more information on this part of Khajiit lore, I have the UESP open.
Khajiit legends and traditions say that only one mane can be around when one is born. Much of the information about the Mane revolves around legends, so these may just be legends. They are born under a rare alignment of the moons Masser and Secunda when, according to legend, a third moon actually appears. Khajiit tradition and legends seem to mention reincarnation when it comes to how the Mane is born, as well.