Final answer:
The percussion instrument featured in Richard Strauss's Also sprach Zarathustra is the timpani, which creates a powerful and dramatic sound.
Step-by-step explanation:
When listening to the excerpt from Richard Strauss's Also sprach Zarathustra, the percussion instrument that can be heard is the timpani (kettledrums). The timpani produce a resonant and dramatic sound that builds the monumental opening sequence of the piece, which has become famously associated with the film 2001: A Space Odyssey. This piece is an example of Romantic music, which aimed to express the full range of human emotions, from anger and passion to pleasure and joy.