John Stig Claesson (2 June 1928 – 4 January 2008), also known under his signature Slas, was a Swedish writer, visual artist, and illustrator. Claesson was born on 2 June 1928 in Huddinge, south of Stockholm. He attended the Royal Swedish Academy of Arts between 1947 and 1952, during which time he began to illustrate Swedish literature such as the novels of Per Anders Fogelström. Claesson was the father of actor Leif Claesson. The elder Claesson died on 4 January 2008 in Stockholm.