Penna started the trend many years ago and other executive search firms have taken on management consultancy businesses. Heidrick's takeover of Senn Delaney in 2013 springs to mind. I'm not sure if these are long term bets: although executive search shares some similarities with consultancy, and indeed ex management consultants are found in executive search firms, but they have very different business models which makes for uneasy bedfellows.