This is the statue of King Konstantine at the entrance to Pedion Areos which used to be the military marching ground but is now a huge park.
Why there is a statue to this guy is beyond me. His disagreements with Venizelos ripped the country in half and later he lost two wars in Turkey and died in exile.
If Konstantine had his way Thessaloniki would be Bulgarian. (Venizelos pulled rank and captured the city two hours before the Bulgarians showed up to do the same).
He was pro-German in WWI and basically caused the Asia Minor Disaster which led to the burning of Smyrna and the end of the Greek presence in what is now Turkey,
 where Greeks had lived since ancient times.
If there was anyone to not build a statue to it would be him. Half the country still hates him. (The other half hate Venizelos and he got an airport named after him).
I suppose they want to keep the royalists happy and nobody comes here anyway except to walk their dogs.
The park had a big sign about going through a 100 million euro renovation with meandering rivers and new flora but last time I went there was about 40 feet of 'river' and the pump was broken so it was empty.
So for now lets skip this park and continue down Patission street. By the way, if you want to catch the orange KTEL buses to Sounion, Rafina, Marathon and other places in Attika this is where they leave from. The Thessaloniki buses are across the street.