Casca was loyal to whom in Julius Caesar?

Casca, a tribune, was loyal to the Roman people and felt that his duty was to kill Caesar to save them from themselves.  He felt that the Romans' love of Caesar was fanatical.  As for Caesar, Casca had little time for his histrionics.  Asked to describe the scene where Caesar refused the crown three times after Antony offered it, Casca described Caesar's actions as "mere foolery" (Act 1, Scene 2, line 236).  He mentioned that he thought of laughing as he watched, but refrained, "for fear of opening [his] lips and receiving the bad air" (Act 1, Scene 2, line 248).

In relaying the story in this way to Cassius and Brutus, Casca shows himself to be an early conspirator against Caesar.  Soon after, Casca will work with Cassius to develop the assassination plot and will, in fact, be the first to stab Caesar when the plot comes to fruition.