Just Bind
your Human
property to the Hero
property on your control:
<wpfApplication1:UcHeros Hero="{Binding Human, Mode=OneWayToSource}" />
Try using a OneWayToSource Binding
if you just want to read the value and not update it.
UPDATE >>>
As @Killercam suggested, try setting the default value for your property in the declaration instead of the constructor:
public static readonly DependencyProperty HeroProperty = DependencyProperty.
Register("Hero", typeof(string), typeof(UcHeros),
new PropertyMetadata("Spiderman"));
If that still doesn't work, then you've got something else going on there.