The people finally overthrew the oppressor who had ruled them cruelly for years.

oppressor 是由动词 oppress（压迫）加上名词后缀 -or 构成的名词，表示"实施压迫的人或组织"。oppress 由前缀 op-（表示"对抗"）和 press（压）组成，字面意思是"压制、压迫"。oppressor 指"压迫者、暴君"。