Stefanos "Klaus" Athanasiadis (Greek: Στέφανος "Κλάους" Αθανασιάδης; born December 24, 1988 in Lakkoma, Chalkidiki) is a Greek professional footballer who plays currently for Maccabi Haifa as a striker.
Athanasiadis joined PAOK's junior academy in 1996. After a very short spell at Hertha BSC in Berlin (Germany) in his youth he returned to PAOK and got his nickname Klaus. Besides one year as a loanee to Panserraikos in the 2009/2010-season he played his whole career in Greece at PAOK. During his seven seasons at PAOK since he returned from Serres he became the first ever PAOK-player to score a hat-trick in an European match on September 18, 2014 against Dinamo Minsk from Belarus. Athanasiadis is the current topscoring player for PAOK in European competitions with 20 goals.
In the summer of 2017 he moved to Israeli club Maccabi Haifa. He played 20 games in Israel scoring just one goal before moving back to Greece in September 2018 to join PAS Giannina. In 2020 he signed for Apollon Larisa after being unemployed for over a year.
Athanasiadis was capped 12 times for the Ethniki without scoring a goal.