Ghosn, Zetsche, Marchionne - who will go down as the most successful?

Born within 21 months of one another, Carlos Ghosn, Dieter Zetsche and Sergio Marchionne are all running up against retirement age now.

Ghosn, the youngest, turns 64 next week but has signed on for another four years as Renault's CEO. Marchionne and Zetsche have contracts that expire next year when each will be 66.

It's been a remarkable run for the Great Triumvirate — three of the longest-serving auto company CEOs in history.

They're a new breed of European boss — communicative, even breezy, brilliant for sure, numbers-oriented, goal-obsessed, and dare we say ... American in style.

Zetsche cut his teeth running Freightliner in the U.S. in his thirties. Ghosn became president of Michelin North America at 35. Marchionne launched his business career in Canada.

For a nerdy auto industry history buff like me, it's kinda cool to conjecture about who will go down as the best and most successful. All have singular achievements to their name. Zetsche has had BMW on the run in recent years, Marchionne saved Fiat and Chrysler, and Ghosn did what we didn't think possible — gainfully combining Renault and Nissan. (We were sure Daimler and Chrysler made a better match.)

By the way, the DCX flop doesn't get laid at Zetsche's feet. He did well by Chrysler, and as Daimler's chief he has far outperformed his predecessor, the highly overrated Juergen Schrempp.

Ghosn's predecessor, Louis Schweitzer, was anything but overrated. That philosopher-king, a seemingly ego-less CEO, revived Renault against all odds and acquired control of Nissan against even greater odds. But Schweitzer's greatest accomplishment? Discovering and deploying Carlos Ghosn.

As for Marchionne, all you need do is consider the flat-footed chiefs who preceded him at Fiat. When he took over in Turin in 2004, he looked like one more in a line of disappointments. But as we reported last week, the man has been a virtuoso of value creation.

So who is the best of the three — "Le Cost-Killer", "il dottore" or Dr. Z?

Well, first we need to see how the stories end because, legacywise, you can louse things up in those last couple of years. Sticking around for a victory lap might seem like a good idea for executives regularly told they are irreplaceable. But victory laps can be treacherous.

Lee Iacocca should have retired from Chrysler at 65, but waited until he was 68. In 1999, Volkswagen CEO Ferdinand Piech was named Car Executive of the Century. He left the management board in 2002 at 65, then became an overactive supervisory board chairman until his controversial exit in 2015 at 78.

History suggests that exiting at age 65 is about right. Schweitzer, by the way, retired at 63.

As things stand, Ghosn, Zetsche and Marchionne are headed for the Hall of Fame. But as Hall of Famer Yogi Berra said: It ain't over till it's over.