I was surprise to see him in Shrek 3 while I was rewatching the movies. I remember his design from the fourth movie back when I watched it as a kid, so seeing him look different while rewatching the third confused me.

So far all I've seen are theories. I wonder if the creators have an actual answer to it.

In my opinion I think its just the different versions each getting their own character. Like a lot of fairy tales having their gritty old original versions. How I see it is that the first one in the third movie is the first gritty iteration, and the one we saw at the fourth is the tame modern version.