We believe he was born in June 17, 1890. He lived in France from a young age. He has a French-Basque heritage, and we know his formal surname in France was Olis Velasco y Nevarro (or possibly Olis Velasco et Nevarre).
Growing up, I had heard tales of Marcel coming from a royal family, and that his family tree is displayed on the wall in the main library in Paris. Knowing that tales become taller when told to a child, I am going to assume, without investigating, that these are exaggerated. Someday, I hope to travel to Paris to see for myself.
To the best of my knowledge, Marcel had only one sister. I don't know much about her except that she became a Nun in the Catholic Church, and lived her life serving the Church.
We know that Marcel studied art at the Sorbonne University. Shortly after graduating, he traveled to South America to the Straits of Magellan to construct a statue there. He had won this opportunity from a competition at the University. He was only 16 years old.
During World War I, he became a mercenary pilot for Belgium. One of the most interesting things I found was that his pilot's license number was in the 300's. This translates to him being a very early adopter in aviation.
I will close with a very interesting story... I came across a pen & ink drawing done by Marcel that I vaguely recalled seeing before. My dad explained that Marcel was shot down & captured by German troops during WWI, and that he had escaped by disguising himself as a peasant. Later in life, he created this pen & ink drawing from memory. It captures the German prison camp - which strongly resembles a castle - and a small figure in the foreground carrying a shepherd's staff. Fascinating! Isn't it!