In a fugue, what is the initial statement of the main theme called, and in what key is it typically played?

In a fugue, the initial statement of the main theme is referred to as the subject. This theme is typically introduced in the tonic key, establishing the primary tonality of the piece. The subject serves as the foundational material for the fugue, and its presentation in the tonic key ensures that listeners can easily identify and relate to it. This clear establishment of the subject in the tonic key allows for effective development and variation throughout the composition as it reappears in different forms and keys, contributing to the complexity of the fugue.

The other options do not appropriately describe the function and role of the main theme in a fugue. The answer is specifically concerned with the terminology surrounding the initial presentation of the main theme and its tonal context, which aligns perfectly with the description of the subject in the tonic key.