The demonic figure holding the wheel is Yama, the Lord of Death.
The "Dictionary of Pali Proper Names" [Pali Text Society] has the following;
The god of death. When beings die they are led before him to be judged according to their deeds. Birth, old age, illness, punishment for crime and death, are regarded as his messengers, sent among men as a warning to abstain from ill and do good. Yama questions beings brought before him as to whether they have seen these messengers and profited by them. If the answer is in the negative, the nirayapalas [guardians of hell] take them away to the different hells.
...[Buddhaghosa] says that Yama is a vemanikapetaraja, who sometimes enjoys all the pleasures of heaven, in a celestial heaven, in a celestial mansion, surrounded by kapparukkhas [heavenly trees] and at other times experiences the fruit of his kamma. He is a good king.
This last may seem strange. But it seems that Yama is actually reluctant to throw beings into hell and is not at all vengeful or arbitrary. He is probably best thought of as a cosmic bureaucrat or functionary for the workings of kamma.
The best passages describing Yama is found in the Majjhima Nikaya, sutta 130, the Devaduta Sutta.