Simon the Cyrenian
Simon the Cyrenian is the speaker of the poem. He is a character from the Bible, and the poem is dedicated to his bearing of the cross of Jesus. Despite the skin color of Simon not being mentioned in the Bible, in this poem he is a black man. This is not unusual because the poet is also a black man, and this interpretation of the character is used for commentary on racism.
Jesus Christ
Despite not being an active character within the poem, it is still mostly dedicated to the persona of Jesus and the Crucifixion. The influence and the power of Jesus on the character of Simon is depicted from the very beginning. He didn't call upon Simon, but Simon still heard His word, and at the end, made the decision to bear the cross solely because of pity and love for Jesus.
The Roman soldiers
The Roman soldiers and Rome in general are the main antagonists in the poem. They force Simon to bear the cross of Jesus, and Simon refuses, inferring that they only do it because he is a black man. In the final stanza, the cruelty of Rome is mentioned when Simon describes the lash and stone used by Rome.
