Russ T.
From Homestar Runner Wiki

With puppet Homestar
Russ T. Cobb is an Atlanta-based recording engineer. He is credited (as a member of Ruby Red Productions) for mixing work on the first three strongbad_email.exe DVDs, and the September 2003 CD mix of Strong Bad Sings and Other Type Hits.
Cobb has also done mixing work for artists including Puffy AmiYumi, Bowling for Soup, My Chemical Romance, and Yuji Oda.