There will also be a familiar face in the Ulster set-up in the form of former teammate BJ Botha and Muller can't wait to get started.
He said: "David came to see me during our pre-season and I made my decision two or three days later.
"It didn't take long for me to make up my mind. I was convinced that I wanted to come.
"When I met David I saw a guy who was genuine - what you see is what you get which means I have a lot of respect for him. The way he handled the whole thing impressed me.
"Normally I look at people's character and make decisions based on what I see. What I saw in him played a big part in pulling me towards this place.
"I wanted a challenge - most rugby players love a challenge - and to experience something different.
"My hope is that as a result of my experience and knowledge of the game after 12 years with Sharks I can help Ulster."