Sonic, also known as Speed-o'-Sound Sonic, is a recurring character in One Punch Man known for his incredible speed and rivalry with the series' protagonist, Saitama. Here’s a summary of his character:

1. Incredible Speed: Sonic's primary ability is his superhuman speed. He is one of the fastest characters in the series, capable of moving and attacking at speeds that make him nearly impossible to see or catch. His speed is not only useful in combat but also in evading attacks and traversing long distances quickly.

2. Obsessive Rivalry: Sonic is intensely obsessed with defeating Saitama, whom he sees as his ultimate rival. This obsession stems from their first encounter, where Sonic was easily defeated by Saitama despite his own impressive speed and skill. Sonic's rivalry with Saitama is a recurring theme in the series, often leading to comedic situations as Sonic attempts to challenge or outshine Saitama.