Pindarus appears in just a small part of Shakespeare's Julius Caesar, so there's not a great deal to explain about him. The enotes Study Guide on the play says the following:
Pindarus is a servant to Cassius. He incorrectly reports to Cassius that Titinius has been captured. Cassius then promises to give Pindarus his freedom on the condition that Pindarus will assist Cassius in his suicide. As soon as Cassius's death is accomplished, Pindarus flees from the Romans.
Pindarus enters the stage in Act 5.3.9 and warns Cassius to flee because Antony's army is near:
Fly further off, my lord, fly further off!
Mark Antony is in your tents, my lord,
Fly, therefore, noble Cassius, fly far off!
But Cassius brushes him off, saying the hill he is currently on is enough of a retreat. Pindarus is used here and again when he flees rather than staying after Cassius is dead, to highlight Cassius's nobility concerning his death. Pindarus addresses him as noble, and for most of the play Pindarus would have been mistaken. But here his address is appropriate, for Cassius will die a death worthy of a Roman.
When sent to a better vantage point to watch Titinius's progress, Pindarus misinterprets what he sees when soldiers surround Titinius. In the muddle of battle it is difficult to determine whose side soldiers are on--after all, they are all Romans. This is not accidental. This emphasizes the fact that both sides are Romans, and Romans wouldn't be fighting Romans if the conspirators hadn't assassinated Caesar.
Pindarus's misinterpretation also gives Cassius an occasion for death. Cassius recounts the history of his relationship with Pindarus (captured him, saved his life by making him his slave), and offers to set him free if Pindarus will kill him with his own sword.
Pindarus is practical and pragmatic, and this is not his fight. He exits, but also mourns his master's death, revealing another side to Cassius's character, a side even a slave could be fond of.