Sigurður Ágúst Þorvaldsson (born 25 November 1980) is an Icelandic basketball player and a former member of the Icelandic national team. During his career, he won the Icelandic championship and the Icelandic Cup four times each. He was a four-time Úrvalsdeild Domestic All-First Team member and in 2005 he was named the Úrvalsdeild Domestic Player of the Year. In 2010, Sigurður was found guilty of rape and sentenced to two years in prison.