What is a 19th Century Roman Gothic structure in the Washington National Cathedral?

Washington National Cathedral has a sculpture of Darth
Vader on the northwest side of the Cathedral. The villain from the Star Wars franchise
was placed high on the northwest tower of the Cathedral, fulfilling the role of a
traditional grotesque. The creation was added in the 1980’s after the architects decided
to have a contest for children to create the grotesque for the tower. The sculpture of
Darth Vader can be found at
http://www.nationalcathedral.org/about/darthVader.shtml

A
grotesque is a decorative figure that originated in the style of Ancient Rome. It then
spread to Italy and Europe and since the 18th century a grotesque has been used to
describe a strange, ugly, unpleasant, shape or form. Grotesque forms are seen on most
Gothic-style buildings.