Complex sentence: In 1919, the Italian designer Thayaht started designing his most famous piece, the TuTa, which he called "the most innovative, futuristic garment ever produced in the history of Italian fashion".
Split into simpler sentences: In 1919, the Italian designer Thayaht started designing his most famous piece. The TuTa, which he called "the most innovative, futuristic garment ever produced in the history of Italian fashion".