The GCA was signed into law by President Lyndon B. Johnson on October 22, 1968, and is Title I of the U.S. federal firearms laws. The National Firearms Act of 1934 (NFA) is Title II. Both GCA and NFA are enforced by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).

Based on this passage, who signed the gun control act of 1968? Let's think fast. Stream of consciousness:
To answer the question, consider the following: The GCA was signed into law by President Lyndon B. Johnson on October 22, 1968, and is Title I of the U.S. federal firearms laws. So the final answer is President Lyndon B. Johnson.