To Simeon Oka and all of you, After a detailed analysis of the life and work written by Dr. P. Stefanović, I have found myself in a difficult situation to write these introductory words. What to say about Professor Simeon Oka? However, I am happy and satisfied with the fact that I have known Prof. Simeon Oka for decades. During the meetings, exchange of views and opinions, mutual understanding and misunderstanding, I have had the pleasure of meeting and knowing him as a person dedicated to science, dedicated to contribution of scientific and technical minds in Serbia (and not only in Serbia). Uncompromising, persistent, serious, conscientious, gifted with knowledge and understanding of knowledge as a spiritus movens of the progress of the brotherhood of men, deeply rational and efficient, Prof. Oka has been and still is a man of high moral and scientific qualities. He did not destroy the bridges - he built them in the scientific world. Whatever he accepted to do - he did it in his way. With these words, on behalf of the Society of Thermal Engineers of Serbia (STES) Prof. Simeon Oka, the holder of the highest awards of the Society of Thermal Engineers of Serbia (already made), has become the first person in Serbia granted with this special number of the Serbian (and International) Journal Thermal Science. We wish him good health, family happiness and further successful work.