Who is the acquaintance of Ellen and Johnny forced to serve?  Answer the above question based on the context below:  Adventurer Johnny Weissmuller is roped in by Egyptian archaeologist Ellen Marsten to traverse the African jungle of Baku. They seek to rescue an acquaintance, Marro, from his captors, pygmies known as the "Moon Men". The Moon Men are devoted to a "Moon Goddess" Oma, who is apparently an immortal whose only weakness is sunlight. Marro is chosen to be Oma's chief religious official. After being joined by Marsten's friend Bob Prentice, the team of Weissmuller, Marstern, and Prentice, set off for Baku. They find Marro and urge him to escape. However, he dies the moment he steps outside the parameters of the jungle. Interrogating a pygmy Damu, Weissmuller learns that Marro was fed a voodoo potion that would kill him once he tried to escape Baku. Just then, the Moon Men overpower the team and capture them. Prentice is selected to take over Marro's position, while Weissmuller and Marstern are brought to Oma's temple. There, they are stopped by Santo and his right-hand man Max (Frank Sully). The evil duo command Weissmuller to lead them into the temple. They meet Oma and also find loads of precious stones in the building. Knowing that not everybody can leave Baku, Weissmuller sacrifices himself for the rest. He asks Prentice to contact the police as soon as he gets to the mainland. Santo pockets a large amount of the jewels and turns to flee. The Moon Men stop him, letting loose a pride of vicious lions. Santo and Max are gorily killed, while the rest manage to escape.
The answer to this question is:
Oma