He has no name and but narrates the situation in the illusionary world seen through Tomoya's dream while referring to himself only as "Me". He has his body created by the girl out of garbage so that he can be with her. The body is about half the girl's height. He can't talk as he is created without a mouth, so relies on body language to communicate with the girl. Unlike most characters in the series, he is created via CGI. (Source: Wikipedia)

Spoiler

In After Story, It is revealed that the Garbage Doll is Tomoya in a world after Ushio's death, as well as the girl being his daughter, Ushio. The last we get to see of the Garbage Doll and the girl is when the Imaginary World is supposedly destroyed.