His most famous book is The Fifth Law of Robotics, published in 1983, the title being a reference to Isaac Asimov's Three Laws of Robotics and the fifth law being that a robot must know that it is a robot. 
The science- fiction fan club "Fantastica" was founded in 1997 in the town of Kardzhali, in the south of Bulgaria by him. The club has a page in Nov Jivot (New Life) - the official newspaper of Kardzhali - and up to late 2003, it had published over 60 issues. He also edited the magazine Kosmos.
He was also organizer and kind host of the annual Bulgarian science-fiction festival "The 2002 Bulgacon", which took place in Kardzhali. The festival was attended by over 900 participants.
Kesarovski committed suicide in 2007 by jumping from a seventh-storey window of a hospital in Kardzhali.
- "Една запалена свещичка за Кольо Кесаровски". Kulturni Novini. 23 August 2008. Retrieved 4 December 2009.
- "The Bulgarian Laws of Robotics". Blog of V.D. Ivanov. 16 June 2011. Retrieved 22 June 2011.
- "Приключи Националния конкурс за научно-фантастичен разказ". Kulturni Novini. 10 November 2007. Retrieved 4 December 2009.
- "Шест месеца без писателя Никола Кесаровски". Kulturni Novini. 1 March 2008. Retrieved 4 December 2009.
- "Отиде си Никола Кесаровски". Darik News. 29 August 2007. Retrieved 4 December 2009.
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