Which of the following best defines a sycophant?

A sycophant is best defined as someone who acts obsequiously toward someone important in order to gain advantage; this behavior often includes excessive flattery or ingratiating actions. The term highlights a sense of self-serving behavior, where the individual, often called a "toady," seeks to please others, especially those in positions of power, to further their own interests.

In this context, a toady characterizes the essence of a sycophant by emphasizing its focus on servility and flattery, which contrasts with the other choices. A loyal friend implies mutual respect and honesty rather than self-serving flattery, a critic points to a more adversarial or analytical stance that doesn’t align with the sycophant's ingratiating nature, and a neutral observer suggests a lack of bias or personal interest, which stands in opposition to the sycophantic desire for personal gain at the expense of independence or honesty. Thus, the choice that best encapsulates the characteristics of a sycophant is indeed the one describing a toady.