Final answer:
The information provided does not directly answer the question about which character's countenance seems to disturb Caesar. The texts reference historical figures like Cleopatra and Catiline but do not address the countenance of a character disturbing Caesar.
Step-by-step explanation:
The countenance that seems to disturb Caesar upon his return from the race, according to the context given, is not directly mentioned in the excerpts provided.
It would be inaccurate to speculate given the information at hand.
The provided texts discuss various historical figures and their actions, like Catiline, Cleopatra, Antony, Gracchus, and Caligula, but do not directly mention a character's countenance that disturbs Caesar.
Furthermore, the Julius Caesar referenced in the student's question is likely the character from Shakespeare's play and not the historical Caesar, which means that an answer would require specific knowledge from the dramatic work Julius Caesar by William Shakespeare.