Not all CEOs are created equally.
Executive recruitment firm Kittleman ranked the top 50 CEOs based on their impact on the average monthly revenue generated during their tenure as the top executive at their respective companies.
Apple Inc. (AAPL) - Get Apple Inc. (AAPL) Report CEO Tim Cook topped the list, with average monthly revenue growth of nearly $1.6 billion throughout the 77 months that he has been at the top of the world's most valuable company.
The cash generated under Cook is far and away the most of any other CEO on the list.
Lary Merlo of CVS Health (CVS) - Get CVS Health Corporation Report , Lowell McAdam of Verizon Communications Inc. (VZ) - Get Verizon Communications Inc. Report , Sundar Pichai of Alphabet Inc. (GOOGL) - Get Alphabet Inc. Class A Report , and Jeff Bezos of Amazon Inc. (AMZN) - Get Amazon.com, Inc. Report rounded out the top five.
Nearly half of the companies that were scrutinized, 24 of 50, saw revenue impacted when the CEO was approximately four to eight years into the position.
Only 10% of the companies on the list had female CEOs at the helm, four of which -- Hewlett Packard (HP) - Get Helmerich & Payne, Inc. (HP) Report , Lockheed Martin (LMT) - Get Lockheed Martin Corporation (LMT) Report , General Motors (GM) - Get General Motors Company (GM) Report , and General Dynamics (GD) - Get General Dynamics Corporation (GD) Report -- grew significant revenue in five years or less.
Mary T. Barra of GM received a special shout out in the report for turning around GM with average growth of $218 million per month after just 48 months considering the company filed for bankruptcy in 2009.
Here is the full CEO list with rankings.