One of the first digital motion capture performances that captured audiences in theaters was Andy Serkis' Gollum. Rather than being a man wearing extensive prosthetics or being an entirely animated character, Gollum was Andy Serkis. All the physical movements were his, but the character of Gollum was physically created around him using digital technology. It's a unique role for that reason, but also because it meant the actor had to spend most of his time on set walking around on all fours.
Gollum doesn't walk like a person, but more like a gorilla. He uses his arms and legs to move around, and since his movements were going to be used to make Gollum real, Andy Serkis apparently spent quite a bit of time perfecting these movements. He recently told The Guardian that he actually went for walks this way to practice the movements. This apparently got slightly awkward when he would run into other people while doing it. Serkis explained,
I used to walk on all fours off set when we were filming Lord of the Rings. I spent a lot of time in preparation for that [as Gollum]; I would go off for walks on all fours for hours. I did occasionally come into contact with other people, so I just had to pretend I was looking for something. It’s fair to say that’s pretty method.
One can only imagine wandering around the production of the film, or just a random place in New Zealand, and discovering Andy Serkis crawling around on all fours. If it happened more than once to one person they had to wonder why the actor was seemingly always dropping things and then having to look for them on the ground.
At the same time, it all certainly worked. Gollum worked and felt like a real character even though so much of what we saw on his face was created digitally. Andy Serkis' performance was just as "real" as any other in many ways, and perhaps that's why it all worked so well. Gollums face was not real but the expressions were based on those that Andy Serkis did, and the same is true for the physical movement of the character. If nothing else, you have to figure the guy needed to practice that walk if only to avoid pulling a muscle on set.
The role of Gollum would make Andy Serkis the preeminent motion capture actor of a generation. He would go on to work on the the Planet of the Apes franchise, Star Wars: The Last Jedi, and even direct a version of The Jungle Book where all the animal performances were done via motion capture technology. Andy Serkis paved the way for many others that have followed after him.