BlackRock just promoted the head of its $1.9 trillion ETF business and it could mean he's a potential successor to CEO Larry Fink

BlackRock chief executive Larry Fink stirred more speculation about his successor on Wednesday when he promoted Mark Wiedman, formerly head of one of the firm's fastest-growing businesses.

Wiedman, who ran the firm's $1.9 trillion exchanged-traded-funds business and index investments known as iShares, is now the head of international and of corporate strategy, Fink said in a Wednesday employee memo obtained by Business Insider. In his new role, Wiedman will focus on "high-growth markets" in Europe, the Middle East, Africa, and Asia-Pacific. He'll also oversee marketing, which is led by former BuzzFeed chief marketing officer Frank Cooper, who will report to both Wiedman and Fink.

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"The changes transforming our industry put a premium on strategy to drive growth, on unifying our focus on international markets, and on using our brand to drive our business," Fink wrote in the memo.

Wiedman has overseen explosive growth in ETF platform iShares, which saw a record $44 billion in new money last month. He left a previous role overseeing corporate strategy in 2011 to lead iShares, which has expanded its assets by 14.8% annually on average.

Fink has made no public statements about retiring, but Wiedman's promotion fueled talk of who could replace the BlackRock co-founder. Other potential successors include another two other Marks - head of active equities Mark Wiseman and head of Americas Mark McCombe - and two Robs, president Rob Kapito and chief operating officer Rob Goldstein.

Rich Kushel, who runs the multi-asset strategies and global fixed income groups, is another potential contender to replace Fink.

"If you think about the future - how they talk about the future of their company and where the growth is coming from, a lot of the technology initiatives they've been growing, like Aladdin for wealth [management] - it all seems to come back to iShares and how they sell it and use it in more creative ways," Patrick Davitt, an analyst at Autonomous Research, told Business Insider. "Through that lens, it feels like it makes sense to have the person who's been building and running that business to be the heir apparent" to Fink.

Salim Ramji, the firm's head of US wealth advisory, is replacing Wiedman as head of iShares and index investments. Martin Small, the US head of iShares, is taking over Ramji's role.

In Wednesday's memo, Fink hinted at more changes "we'll make later this year" at the $6.4 trillion asset manager.

Wiedman's move, along with references of more to come, comes as Wall Street has grappled with how to replace founders and longtime leaders. Blackstone, for example, elevated former real estate head Jon Gray to president last year after grooming multiple leaders to run the world's largest private equity firm. Goldman Sachs had two co-presidents under CEO Lloyd Blankfein, before one retired this spring, leaving David Solomon to replace Blankfein this fall.