Jeffy is a popular character from the YouTube channel SuperMarioLogan, created by Logan Thirtyacre. He is known for his distinctive blue helmet, diaper, and childlike behavior. Jeffy often engages in humorous and chaotic antics, which appeal to a younger audience. The character is portrayed as a mischievous and sometimes annoying figure, often causing trouble for other characters in the series. His catchphrases and silly actions contribute to the comedic style of the videos, making him a memorable part of the SuperMarioLogan franchise.