gistfile1.py

class MyForm(form):
    def __init__(user, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)
        self.fields['character'] = forms.ChoiceField(
            choices=[(c.id, c.name) for c in Character.objects.filter(...)]
        )

# In view
def my_view(request):
    form = MyForm(request.user, ...)