Trompowsky Attack

The Trompowsky Attack is a chess opening that begins with the moves:
White prepares to exchange the bishop for Black's knight, inflicting doubled pawns upon Black in the process. This is not a lethal threat; Black can choose to fall in with White's plan.
The Trompowsky is a popular alternative to the more common lines after 1.d4 Nf6 beginning 2.c4 or 2.Nf3. By playing 2.Bg5, White sidesteps immense bodies of opening theory of various Indian Defences like the Queen's Indian, King's Indian, Nimzo-Indian, as well as the Grünfeld Defence.
The opening is named after the one-time Brazilian champion Octávio Trompowsky (1897–1984) who played it in the 1930s and 1940s. However, chess master William Allen Ruth developed the opening simultaneously in the 1930s, and was well-known by locals in Pennsylvania as the "Ruth Opening". The Trompowsky has also been called "The Zot".
Julian Hodgson and Antoaneta Stefanova are among several grandmasters who often employ the Trompowsky. World Champion Magnus Carlsen has occasionally employed the Trompowsky, notably in the first game of the 2016 World Chess Championship against Sergey Karjakin.
Main lines.
Black has a number of ways to meet the Trompowsky, some of which avoid doubled pawns, while others allow them. The most common Black responses are discussed here.
1.d4 d5 2.Bg5.
White can also play 2. Bg5 after 1. d4 d5. This is known as the Pseudo-Trompowsky, Hodgson Attack, Levitsky Attack, Queen's Bishop Attack, and Bishop Attack, and is covered in ECO code D00. Play can transpose to the Trompowsky if Black plays 2...Nf6.