Who leads Napoleon around the farm acting as his trumpeter?

The character that leads Napoleon around the farm and acts as his trumpeter is indeed the black Cockrel. This character serves a significant role by announcing Napoleon's presence and effectively acting as a herald for his authority. The black Cockrel symbolizes the way propaganda is used in the story; it conveys information that serves to elevate Napoleon’s status and emphasizes his power amongst the other animals.

Other options do not fit the portrayal of this specific role. For instance, while other pigs are influential and play various roles throughout the story, they do not serve specifically as trumpeters for Napoleon. Similarly, a black rooster, though similar in appearance to the correct choice, does not specifically reference the character known for this role in the narrative. Lastly, Boxer, the hardworking horse, contributes significantly to the farm but does not take on the role of a trumpeter for Napoleon; his character represents loyalty and labor rather than the propagandist function depicted by the black Cockrel.