Who is the herald in shrek?

The Herald in Shrek is Lord Farquaad, the ruler of Duloc. He's the one who announces Shrek's arrival and the dragon's impending doom in his pompous and theatrical way.

While he's not traditionally a "herald" like the ones in medieval tales, he acts as one in the movie by being the voice that proclaims Shrek's arrival and introduces the events to the audience.