From Homestar Runner Wiki
R. Craig Zobel is a friend of the Chapmans and a shareholder in Homestarrunner.com. He currently resides in New York. He and Mike wrote the original Homestar book back in 1996 (which was remade as Strongest Man in the World for Homestar Runner's ten year anniversary). He also helped write "Where's The Cheat?" and "Homestarloween Party". Zobel designed the covers for the strongbad_email.exe DVD box set and appeared in a short film in the DVD bonus feature "Puppets on the Road."
Craig has provided the voices of Cherry Greg and the Kevin who leaves a message on Marzipan's Answering Machine Version 6.0. It was revealed in Issue #21 of Wonkavision magazine that Coach Z was named after Mr. Zobel.
He directed the feature film Great World of Sound (2006), which was produced by Missy Palmer and executive produced by the Brothers Chaps. He's also signed a deal with Plum Pictures to produce his next film, Turkey in the Straw. 
Mentioned in the commentary for replacement by Matt, "[Craig's] favorite thing ever on our website is … where Bubs attacks Strong Bad."