Complex sentence: Marker was born Christian François Bouche-Villeneuve, in Paris, France, 29 July 1921, yet other sources and himself claim that he was born in Ulan Bator, Mongolia.
Split into simpler sentences: Marker was born Christian François Bouche-Villeneuve on 29 July 1921. Some sources and Marker himself claim that he was born in Ulan Bator, Mongolia.