Which brass instrument is different from all the others and why?

The French horn is different from other brass instruments primarily due to its unique coiled shape and the use of a rotary valve system, which allows for a wider range of notes and greater control over tone. Unlike most brass instruments that are played with a straight or slightly curved tube, the French horn's design contributes to its distinct warm and mellow sound. Additionally, the player’s hand position in the bell can significantly affect the instrument’s timbre and intonation, setting it apart from others in the brass family.