Final answer:
The first Christian martyr recorded in the Bible as being affected by Saul, later known as Paul, is Stephen, stoned to death in Acts 7:54-60. Saul, who witnessed and approved of Stephen's execution, underwent a dramatic conversion experience later portrayed in art and scripture.
Step-by-step explanation:
The first martyr killed by Saul, who is better known as Paul after his conversion on the road to Damascus, is not explicitly named in biblical texts.
However, the first Christian martyrdom recorded in the Acts of the Apostles is that of Stephen, stoned to death in Acts 7:54-60, while Saul approved of his execution (Acts 8:1). This was before Saul's conversion experience, which is vividly depicted in Caravaggio's painting The Conversion of Saint Paul and in historical accounts such as those by Luke in the Acts of the Apostles.
Regarding martyrdom during Saul's time, the painting The Martyrdom of Saint Matthew by Caravaggio portrays the death of Matthew, although this occurred later and was not associated with Saul. The first large-scale, government-sanctioned persecution of Christians began under Emperor Nero, as mentioned by the Roman historian Tacitus, and included the martyrdom of the apostles Peter and Paul in Rome.
Other early Christian martyrs include Thecla and Perpetua, although their stories are separate from Saul's actions.