Samson, the apparently deaf-mute slave who Rosh steals from a passing caravan, is important to the action and characterization in The Bronze Bow. He plays an important role in the action because when Daniel stages a risky effort to free Joel from the Romans, Samson jumps in to help without Daniel's knowledge. If it had not been for Samson's intervention, Daniel would probably have been killed in the fight and Joel would not have been freed and in fact might have suffered a worse fate than what he already faced.
As far as characterization, Samson parallels both the character of Daniel and the character of Jesus. As such, he is not exactly a foil, but something like a foil. A foil is a character who makes the qualities of a main character stand out more clearly because of the way he contrasts with the character. In the case of how Samson enhances the characterization of Daniel and Jesus, however, it is his similarities rather than differences that help us understand the characters better.
A parallelism exists between Samson's relationship with Daniel and Daniel's relationship with Rosh. Samson shows blind loyalty to an embarrassing degree toward Daniel, and, although Daniel doesn't realize it in the first chapters of the book, Daniel shows that same type of unthinking allegiance to Rosh. Eventually Daniel comes to realize that Rosh is not a worthy leader; at that point, he takes on the leadership of Joktan, Nathan, and the other young men who plan to rescue Joel. Although Daniel believes at this point he is a better leader than Rosh, his near-death experience and the loss of Nathan and Samson show that he has acted as selfishly as Rosh. In fact, Daniel's leadership has been worse than Rosh's, for at least Rosh realized Daniel's scheme was bound to fail. Daniel created a situation that resulted in two of his followers losing their lives. The difference between Daniel and Samson as followers is that Samson never deserted Daniel; he stuck with him despite his ill-conceived venture.
This leads to the second parallel Samson provides, namely a parallel to Jesus. Jesus is the Messiah, but to Daniel and Joel, he is a disappointment because he comes as a servant rather than a king. He speaks quietly and seems deaf to those who are calling for rebellion against Rome. Instead of overcoming the Romans by hatred, he seeks to bring in God's kingdom through love. Samson demonstrates the self-sacrificial love that Jesus showed in the novel but also would show later when he gave his life as a sacrifice for the sins of the world. Samson is what is known as a "Christ figure," that is, a character who sacrifices his own life to benefit someone else, someone who does not deserve it. When Samson sacrifices his own life for Daniel and Joel, he foreshadows what Daniel finally learns from Jesus in Chapter 24: "that only love could bend the bow of bronze."