Inspired by a design in the comics by Alfredo Alcala that showed a future king of Grayskull with a red cape and wearing a green body suit. Later it is insinuated that He-Man will become that King, though Mattel used the image in the bio for the actual King Grayskull (that's why the alternate head is there).
MOTUC Man-At-Arms body and Power Sword
MOTUC He-Man Head, Harness, and Shield
Modified MOTUC King Grayskull Cape
Fan Created MOTUC Bio for KING HE-MAN (Not canon so he can be whatever you want him to be!)
Real Name: N/A
Immediately after returning to Eternia following a long absence in space, He-Man discovered that his father was now dead. As true heir to the throne he took the place of Randor though he initially refused to wear the crown. In deep mourning, the new King He-Man chose to represent the dead with a new darkened set of armor and utilized one of the last body suits created by his departed friend Man-At-Arms. Despite his advancing age and a fresh facial wound (courtesy of his final battle with Skeletor), King He-Man would go on to valiantly defend the honor of Grayskull for many years.