The Eighth Doctor Who was a bit of an odd duck. Appearing on screen only in the TV movie, he was meant to act as a kind of bridge between the old series and a new one, which could appeal to a wider (i.e. American) audience.

A series like that did eventually happen, but unfortunately he wouldn’t be part of it (though he did appear in a lot of non-TV material, such as books and radio plays).  As he was something of a transitional object himself, I thought the bird-like Archaeopteryx would be a perfect fit for the “half-human” doctor.