Final answer:
The quote refers to c. Antony, highlighting how his prominence intensifies when he is with Cleopatra.
Step-by-step explanation:
The quote "Thy luster thickens when he shines by" refers to the character c. Antony in the context of his relationship with Cleopatra. It is meant to convey how Antony's significance or brilliance increases when he is in the company of the illustrious queen.
This type of language and thematic concern can be found in works that focus on the dynamics of historic figures such as Antony, Cleopatra, and Julius Caesar, and is a common aspect of literature that deals with historical romance and political power.