The call sign is a specialized form of nickname that is used as a substitute for the aviator's given name.
Many NASA Astronauts with military aviator backgrounds are referred to during spaceflights by their call signs rather than their first names.
Most call signs play on or reference on variants of the aviator's firstname or surname.
Other inspirations for call signs may include personality traits, middle name, references to historical figures, or past exploits during the pilot's career.
For example, U.S. Navy Lieutenant Kara Hultgreen was originally given the call sign "Hulk" because of her ability to bench-press 200 pounds.