Kurdt Kobain is an alias Kurt Cobain used on occasion. The monkey photograph on the sleeve of the Nevermind album is credited to this name. Cobain also later used the aliases Mr.Poupon and Simon Ritchie (the real name of Sid Vicious) when checking into hotels, to avoid media and fans.
The spelling "Kurdt" originally came from the Teriyaki Asthma compilation, on which the track "Mexican Seafood" appeared. One of those lovely people who think they know things got it wrong.