Complex sentence: The Stronach Group is owned by Canadian horse breeder and owner Frank Stronach, who also was MI Development's chairman and chief executive, a position he gave up in order to run Maryland's racetracks.
Split into simpler sentences: The Stronach Group is owned by Canadian horse breeder and owner Frank Stronach. Stronach was also MI Development's chairman and chief executive, a position he gave up in order to run Maryland's racetracks.