He's been around for a while, but I only recently found out that he is a "he".
She talks to him a lot. I'll hear her babbling on and ask her what she's talking about, only to be informed that she was not talking to me, but to him.
Yesterday I was told that his name is Wilbur.
He is currently "at work and [she's] talking to him on the phone" while she cleans up her legos.
Sometimes he is big. Sometimes he is small. She can pretty much always tell you where he happens to be standing and sometimes it's the most unlikely place...
...considering that no matter what other aspects of him change he is always a cow.