Trafigura's co-founder and chief executive Claude Dauphin, 63, who owns less than a fifth of the firm, stepped down this week to receive medical treatment. Jeremy Weir, who ran the mining and risk management divisions, will take over the firm, putting a 50-year-old Australian geologist in charge of the enterprise with a turnover of $133 billion.

At Gunvor, Russian founder Gennady Timchenko was forced to sell his 43.5 percent share to Swedish co-founder Torbjorn Tornqvist after the United States slapped sanctions on him to pressure President Vladimir Putin over Crimea. Tornqvist, 60, who has long been CEO, now has full control.

Both changes were generally unexpected, and are prompting wider questions of succession in an industry historically known for both its secrecy and its powerful, charismatic leaders whose trading skills and global contacts built the foundation of today's global titans, which also include Vitol, Glencore (>> Glencore Xstrata PLC) and Mercuria.

While most remain reluctant to talk openly about their plans for one day relinquishing control, some say they are grooming future leaders as a generation of traders who were instrumental in the creation of the modern day commodity markets enter their 60s with paper fortunes and a rapidly changing landscape.

"Succession planning is definitely an issue for the banks that finance commodity traders, they're interested in understanding it," a high level source at a trading house said.

Yet while chief executives have in recent years thrown off the cloak of secrecy and become prominent industry figures, the names of those next in line remain, in many cases, largely unknown. Weir had not been on most rivals' radar before this week even though he was a rare executive at Trafigura who gave several public interviews.

Investors and bankers know that the show at the world's largest oil trader Vitol is run by CEO Ian Taylor, 58; at Gunvor by Tornqvist, 60; at Mercuria by CEO Marco Dunand, 51, and Daniel Jaeggi, 52; and at Glencore by Ivan Glasenberg, 57.

The second layer of management is often much less visible.

Vitol's Chief Financial Officer Jeff Dellapina is due to speak at a major industry conference next month - his first major public appearance. Vitol's chief oil trader Mark Couling and chief Trafigura oil trader Jose Larocca have not been interviewed in the business press.

"ANIMAL FARM"

"I have never in over two decades seen much in the way of succession planning. Frankly, trading floors and their management run more like animal farm than General Motors. There is an implicit hierarchy, and that matters," said Chip Register, a long time commodity executive, currently at Sapient Global Markets.

Vitol, one of the best paying firms in the industry which has repeatedly attracted top talent, is owned by its employees none of whom has more than 5 percent, which suggests a collegiate approach to decision-making could be likely.

The firm has been around for 49 years and has had leadership changes in the past, although only under Taylor's leadership since 1995 has it grown into the world's biggest trader.

In the past, other commodity companies that were indelibly linked to founders have faced transitions with mixed results.

One of the industry's oldest firms, agricultural giant Cargill, was run by the founders' extended family for a century until 1960, when Erwin Kelm became the first president not descended from the Cargill-MacMillan families.

More recently, upstart Singapore-listed trading firm Noble Group (>> Noble Group Limited) has struggled to maintain its momentum since founder Richard Elman, 74, handed over the reins in 2010. Several senior leadership departures have followed.

Oil traders have come a long way since the 1970-1980s era of Marc Rich, the godfather of contemporary oil trading, when they disclosed absolutely nothing about what they do. Some still operate that way, such as Westport, Connecticut-based Phibro, a once-mighty oil trading firm that some say would be hard to imagine without its chief Andrew Hall, 62, whose $100 million payday in 2009 caused a furor for then-owner Citigroup. (>> Citigroup Inc)

Dauphin, who started his career with Marc Rich and is not known to have ever given a single interview, introduced annual reports at Trafigura for bondholders which described performance of individual divisions in great detail including volumes, profitability and outlook - something not even many listed firms disclose.

Listed Glencore also publishes detailed reports and unlisted Mercuria, Vitol and Gunvor have also increased the information they disclose in recent years.

BENCH STRENGTH

Trafigura introduced the next generation of leaders a couple of years ago when the company also disclosed it was buying out founding shareholders.

When Glencore went public in 2011, investors got a glimpse into the company's bench strength and newly minted billionaires: Alex Beard for oil, Daniel Mate for zinc trading, Tor Peterson for coal trading and Telis Mistakidis as head of copper. Since then they have made investor presentations and occasionally spoken at media conferences.

"Everyone among our long-standing division heads is a potential CEO," said a source close to Glencore.

Glasenberg, a former coal trader, has run the company for over a decade.

For Gunvor, the most visible executive beyond its CEO is chief investment and operating officer Jerome Schurink, 44, who oversees the firm's expansion strategy and accompanies Tornqvist to meetings such as in Davos.

"We have a succession plan established, consisting of existing management and traders. We review it annually. We also have risk management policies in place regarding such things as how many and which executives are allowed to travel together," a Gunvor source said.

Mercuria benefits to a certain extent by having two founders, rather than one, both of whom are as much as 10 years younger than most of their rivals.

Mercuria has also beefed up its top executive ranks with commodity veterans including Roger Jones, formerly head of commodities at Barclays's (>> Barclays PLC), and chief investment officer Shameek Konar from Goldman Sachs (>> Goldman Sachs Group Inc).

"At the end of the day the bench strength of the trading industry - commodities included - should not be underestimated," said Register. "Significant income opportunities have been driving talent into these markets for decades and there are a lot of great middle managers waiting for their shot at the title."

(Additional reporting by Anna Sussman, Peg Mackey, Alex Lawler, Silvia Antonioli; Editing by Peter Graff)

By Dmitry Zhdannikov and Jonathan Leff