PARIS, April 10 (Reuters) - Bill Ackman's first call before launching his $64 billion bid for Universal Music Group this week was to French billionaire Vincent Bollore, the U.S. hedge fund manager said.

Ackman later told investors the response from Universal's biggest shareholder to his overtures was "music to my ears", adding that Bollore's camp was "intrigued" by his proposal.

"Without Bollore, we don't have a transaction," the founder of Pershing Square Capital Management said of the 74-year-old, who directly and indirectly controls just below 32% of the home to Taylor Swift, Billie Eilish and Kendrick Lamar.

Bollore, who while officially retired continues to be active in business, has effective blocking power over any deal through his direct shareholding and indirect stakes through his family group and his holding in French media group Vivendi.

Bollore's Paris-listed holding group did not respond to requests for comment on Ackman's offer, which is seen by some as a test of the French tycoon's approach to business.

Ackman did not respond to a request for comment. Universal, which has said its board of directors is reviewing Pershing's "unsolicited and non-binding proposal", declined to comment.

After turning around the fortunes of his centuries-old family business, Bollore began building his empire through a series of opportunistic stake-building raids in the 1990s, notably in construction-to-media conglomerate Bouygues.

He then refined that playbook with his takeover of advertising group Havas in the early 2000s, establishing a model of "creeping control" he later deployed in media and has gained a reputation for his hands-on approach.

Universal, where CEO Lucian Grainge has operated with significant autonomy, has so far proved a significant exception.

Bollore's exposure to the world's biggest music company, which he acquired through Vivendi's 2021 spin-off of the business and its Amsterdam listing, is widely viewed as one of his most successful moves.

Bollore gradually asserted his influence over Vivendi, installing allies on the board and tightening his grip.

"He has always known how to unlock value, and he did so in a truly striking way with Vivendi's assets, bringing out the real wealth inside that conglomerate," said Vincent Beaufils, author of a Bollore biography.

BOLLORE GROUP'S COMPLEX OWNERSHIP

While he has reshaped France's media landscape, culminating in Vivendi's takeover of Lagardere and the sale of its logistics arm to CMA CGM, not all of Bollore's bets have paid off.

Vivendi's Telecom Italia (TIM) investment wiped out billions of euros, while a foray into Mediaset triggered a backlash and legal disputes with the family of Silvio Berlusconi and a push into Ubisoft stopped short of a full takeover after resistance.

Forbes estimates that the wealth of Bollore and his family has risen from $5.2 billion in 2017 to $9.8 billion in 2026.

Ackman, who owns a 4.7% stake in Universal and until May last year was a member of its board, is offering Bollore and other shareholders the option of swapping their stock for cash or a stake in a new U.S.-listed entity.

"He will look at it in a very cold and analytical way," said one person who has worked with Bollore. Meanwhile, two industry executives who have dealt with him in the past said Bollore's decisions can be difficult to anticipate.

JPMorgan analysts are among those unconvinced that Ackman will get the response he wants, saying Universal will struggle to recommend a proposal that "materially undervalues" the group.

The key factor shaping Bollore's thinking is his group's highly complex ownership structure, they said in a note on Friday, adding that they expect it to reject the Pershing bid.

"It does not need cash; it has been a buyer, not a seller, of UMG shares; it is unlikely to sell at a discount to fair value; it would not want to reduce its influence; and it has historically favoured a European listing and domicile for UMG".

Bollore's group said it had a net cash position of about 5.6 billion euros ($6.55 billion) at the end of last year.

($1 = 0.8554 euros)