Cadillac’s chief of global strategic development has tendered his resignation, Don Butler became the third senior executive at General Motors’ flagship brand to leave the luxury division in recent months. Butler’s unexpected announcement comes amidst a broader shake-up in senior management throughout the GM global empire. Some senior executives, including Butler, have apparently decided to simply move on, but others have been forced out due to weak performance, in the case of another Caddy exec, because of ethical concerns.