|Full name||Stefanos Klaus Athanasiadis|
|Date of birth||24 December 1988|
|Place of birth||Chalkidiki, Greece|
|Height||1.89 m (6 ft 2 1⁄2 in)|
|2009–2010||→ Panserraikos (loan)||23||(5)|
|* Senior club appearances and goals counted for the domestic league only and correct as of 29 August 2014.
† Appearances (Goals).
Athanasiadis was born in the village of Lakoma, Chalkidiki to a footballing family. Both his father and uncle were footballers. He spent a season with the local team before moving to Thessaloniki. In 1996, Athanasiadis joined PAOK FC's junior academy, initially playing as a central midfielder. His first chance to show his talent came two years later. In the summer of 1998, after participating with the PAOK squad in a youth tournament held in Trieste, Italy, he was approached by the local club and agreed to join their junior team. He was only 10 years old at the time. His stay at Trieste was short-lived, however, as both he and his family could not adapt to their new life. After only a month in Italy, he left for Berlin and his relatives, and joined Hertha's youth squad. Yet after another month in Germany, he left Hertha as well, to return to his native Greece and Thessaloniki.
His ties to Germany earned him the nickname "Klaus", which is also the name on his jersey.
Athanasiadis returned to the junior squad in PAOK in August 1998 and worked his way through the ranks of the academy, showing his scoring abilities and talent with the ball, with the help of junior coach Kostas Malioufas, who established him as a striker. He moved to the Reserve Team in 2004. His hard work under coach Kyriakos Alexandridis was praised in the 2006–2007 season when he became top scorer with 24 goals, with PAOK dominating the Reserve League. His performances earned him a professional contract for three years.
He debuted with the first team on 24 February 2007 in a home match against Larisa, coming in as a substitute, with PAOK losing the match 1–3. Coincidentally, his first game as a starter for PAOK was again against Larissa at the last game of the 2007–2008 season where he scored 2 magnificent goals in the first half, with Larisa defeating PAOK again by 4–3. He also renewed his contract in 2008 for a further 5 years. He was working hard to find a place in the starting eleven, yet was overshadowed by more experienced players like Zlatan Muslimović and Lambros Choutos and was mostly used as a late substitute by Fernando Santos. His most memorable game so far was on 29 November 2008 against Thrasyvoulos F.C. Athanasiadis came off the bench in the 89th minute and went on to score the winning goal four minutes later, winning the match by 1–2.
In 2009 he was loaned at Panserraikos as new strikers arrived at PAOK and he was not a part of coach Fernando Santos' plans. He needed to gain experience as a hot prospect for the future. He got 22 caps in the Football League scoring 5 goals. He scored a goal in the Greek Cup victory 3–1 over Olympiacos.
In 2010-11 season he returned to PAOK. He got 4 European caps mainly as a substitute. He scored his first goal for the season at the first game played in the new AEL Arena as a substitute, giving PAOK a 1–2 victory over Larissa. On 4 August 2011 he scored his first European goal with PAOK in the game with Vålerenga in a 3–0 Europa League victory. On 18 August he scored again, this time against Karpaty Lviv. On November 30 he scored against Tottenham Hotspur F.C., with the second goal for PAOK F.C. in a surprise 2-1 victory at White Hart Lane in the Europa League, when he met a low cross from Giorgios Georgiadis.
In 2012/13 season he scored goals in matches against fierce rivals Aris and AEK while also scoring the equalizer in a 1-1 home draw against Olympiacos. Athanasiadis scored his first hat-trick against Kallithea on 24 January 2013 in a 6-0 win. After the departure of Pablo Garcia he was named vice-captain of the club behind Dimitris Salpingidis, wearing the captain's armbrand on many occasions. On 17 April 2013 he went on to give an assist and score a backheel goal against Asteras Tripoli in the first leg of the Greek Cup semi-finals.
On 8 June 2011 Athanasiadis made his debut for the Greek national football team in a friendly 1-1 draw against Ecuador.
(As of 28 August 2014)