Ezeulu's job as chief priest of Ulu is the main motivation behind all of his actions. His role as chief priest of Ulu gives him the impetus to advise the people in all their actions, to criticize elders and men of title, to take a stance against the Europeans, to send his son to learn the Europeans' religion, and, finally, to punish the people of Umuaro when they fail to respect him (and by default, his deity Ulu).
Nwaka states his opinion vocally and loudly, encouraging people to take his side in opposition to Ezeulu's. Nwaka is willing to voice the opinion that Ezeulu is power-hungry and trying to turn himself into a priest-king. Though clearly successful and aggressive, Nwaka's assertions serve to characterize him as a brash, bold, and perhaps intemperate man.
The characters of Winterbottom, Wright, and Clarke are shaped by the requirements of their social position as British subjects in Nigeria. All three men behave in accordance with their social position: Clarke and Winterbottom as colonial officials, and Wright as a contractor who doesn't have to answer to the British Administration.
For Winterbottom and Clarke, the standards of behavior are high. Clarke chafes against those standards but ultimately acquiesces because he has no other choice. Wright is a contractor; his social position is lower than Clarke's and Winterbottom's, and he feels it gives him the freedom to behave however he wants with impunity. Winterbottom chastises him for sleeping with African women, but Wright doesn't change his behavior. Instead, he ups the ante by whipping one of the unpaid laborers under his charge – he abuses Obika, Ezeulu's son. Clarke likes Wright's honesty and lack of pretension and doesn't want to believe he would do such a thing. Winterbottom, on the other hand, believes that if Wright's moral standards are low.