John Apostolidis was born in 1967 in the coastal city of Volos in Thessaly, Greece. He attended the Theological School of Athens from he graduated in 1988. John continued postgraduate studies at the Theological School of
Aristotle University of Thessalonica. He entered the [[Holy Orders]] when he was [[ordination|ordained]] a [[deacon]] in 1992 and given the name Theologos. Dcn. Theologos was ordained to the [[priest]]hood in 1994. He served as Archdeacon and Secretary of the Diocese of Demetrias before he was assigned as the priest of the Church of St. Konstantinos in Volos. In 1999, Father Theologos was assigned as the priest of the church of St. Sophia at Psychico.
In 2000, Fr. Theologos was appointed
Archigrammateos by the [[Holy Synod]] of the Church of Greece. After his election to the [[episcopate]] by the Holy Synod, Fr. Theologos was [[consecration of a bishop|consecrated]] the Assistant Bishop of Salona on [[October 12]], 2001. In 2003, Bp. Theologos was [[enthronement|enthroned]] metropolitan of the [[Metropolis of Serres and Nigrita]] on [[May 16]], 2003, succeeding Metr. Maximos (Xydas) who had reposed on [[March 5]], 2003.<ref>[http://www.oki-regensburg.de/verst_03.htm Orthodoxia 2003]</ref>