Thalassa Lucas (タラッサ・ルーカス, Tarassa Ruukasu) is the King of Ilusia. He appeared briefly in chapter 142 during the Chopper flashback. He was the bearded, smoking man who showed the photo of Dragon during the Council of Kings 6 years ago in Mariejois. He said that Dragon's thoughts are dangerous and that within 6 more years Dragon would be a great thorn in the World Government's side.
He was only seen in a flashback of 6 years ago. It is unknown if he is still alive and if he still reigns.
Also, Thalassa (Θάλασσα) means "sea" and is the name of a Greek sea goddess who personified the Mediterranean.