What is the world's biggest aircraft?

The Hughes Hercules H-4 by Howard Hugheswas the largest aircraft ever build (excluding aiships and the death star) . Currently the largest aircraft in operation is the Antonov An-225 Mriya, with only2 operational. Encouragingly there are rumours they are going to finish building the third prototype. 

Antonove

Antonov  AN-225 is the biggest aircraft in the world , actually.

That'd be the Antonov An-225 Myria