A former director of the National Security Agency and the first commander of the US Cyber Command, Alexander served as the public face of US data collection during the Edward Snowden leaks, but he retired from public service in 2013.

Alexander is a controversial figure for many in the tech community because of his involvement in the widespread surveillance systems revealed by the Snowden leaks. Those systems included PRISM, a broad data collection program that compromised systems at Google, Microsoft, Yahoo, and Facebook -- but not Amazon.

Alexander was broadly critical of reporting on the Snowden leaks, even suggesting that reporters should be legally restrained from covering the documents.

Alexander's board spot will give Amazon new expertise in defence contracting, an area of focus for the company in recent years.