Complex sentence: Rothschild had been racing his Bugatti and he introduced her to Ettore Bugatti the owner of the very successful car company, who thought that Hellé Nice would be an ideal person to add to the male drivers of his line of racing vehicles.
Split into simpler sentences: Rothschild had been racing his Bugatti and he introduced her to Ettore Bugatti. The owner of the very successful car company thought Hellé Nice would be an ideal person to add to the male drivers of his line of racing vehicles.