What is the leader or initial subject in a fugue called?

In the context of a fugue, the leader or initial subject is known as the "dux." This term refers specifically to the primary theme that is introduced at the beginning of the fugue, and it sets the stage for the subsequent entries that follow. The dux is crucial because it establishes the tonal and thematic foundation of the piece, and it is typically presented in one voice before being followed by other voices that introduce variations or developments of the theme.

The term "exposition" refers to the initial section of the fugue where the dux is introduced and where each voice participates sequentially, presenting the theme. While "subject" can refer to the main theme of a fugue, "dux" is the specific terminology used to describe the initial presentation of that theme. Similarly, "answer" refers to a statement of the subject in a different voice, typically at a different pitch, thereby representing a contrasting counterpart to the dux. Understanding these distinctions is essential for a deeper grasp of fugue structure and terminology in music theory.