Botín, "El Presidente" to his co-workers and the third generation of Botíns to run Santander, was regarded as one of the most powerful and influential bankers of his generation and an astute dealmaker.

The following are some reactions to his death:

MARIANO RAJOY, Spain's Prime Minister:

"I had a meeting with him last week and he was well and in good form. It has been a surprise and a blow.

"He was a man who has been able to make Banco Santander the most important bank of our country."

SORAYA SÁENZ DE SANTAMARIA, Spain's Deputy Prime Minister:

"He was one of the most relevant figures in the Spanish financial system, a person committed to his country."

LUIS DE GUINDOS, Spain's Economy Minister:

"I feel deeply affected by the loss of one of the great bankers of Spain and Europe, of a person with a great talent for business, someone who knew how to combine instinct with a leadership capacity which was exceptional and, most certainly, unrepeatable."

SHEILA BAIR, a Santander board member and former chairman of the Federal Deposit Insurance Corporation (FDIC), a U.S. federal bank regulator:

"He very much managed for the long term, he had a real commitment to the institution and his legacy, he didn't go for the quick buck. He was very astute, but prudent and cautious as well.

"A deal really had to make sense before he would do it ... which is why he was such an astute dealmaker. But he also was good at bread and butter running banks, very good on credit quality, he didn't do ... any of the silliness that you saw with other global banking institutions."

JAVIER MARÍN, CEO of Santander in note to employees:

"Emilio Botín has been the protagonist of a unprecedented transformation process in the international banking sector, which has made Santander the largest bank in the euro zone and one of the biggest in the world.

"We all feel proud to have worked with, and learned from, our chairman and feel committed to continuing his work."

MIGUEL ANGEL REVILLA, former president of Cantabria, whose capital is the city of Santander:

"In the '80s, when his father died, the feeling here in (the city of) Santander was ...: 'When little Emilio arrives, what will become of the bank?'

"He oversaw everything, and Banco Santander had some of the best professionals. He didn't hire friends but asked who was the best."

ANTONIO HORTA-OSORIO, chief executive of Lloyds Banking Group, who worked at Santander from 1993 to 2010 in a number of senior positions, including as head of its British business:

"Emilio was a unique banker, the best of his generation and the driving force behind the success of the bank.

"He was a great mentor to me during my time with Santander and he will be missed by many across the banking industry. My thoughts are with his family."

RON DENNIS, chairman and CEO of motor racing group McLaren. Botín was a keen fan of Formula One and Santander had been a partner of McLaren since 2007:

"Emilio was a consummate businessman, who made Santander what it is today.

"Passionate and charming, he was firm but always fair. I feel privileged to have known him, and proud to be able to call him a friend.

"He adored motor racing - there was no one more enthusiastic in the McLaren garage than he was when a race win was in the offing.

"The world has lost a great man. To his large and loving family, I send my condolences."

LÁZARO DE MELLO BRANDÃO, chairman of Banco Bradesco SA in Brazil, a rival of Banco Santander Brasil:

"A daring and determined leader, he knew how to position the company that he steered through the past 30 years at the top of global financial rankings.

"At the forefront of a successful, well-executed strategy across different markets, Botín made of the banking house founded by his family a global reference for financial services."

ÁNGEL RON, Chairman of Banco Popular, in a note:

"Emilio Botín was an excellent professional and leader, capable of creating an organisation that has helped strengthen the international prestige of Spanish banks. But above all, today we remember a relatable and discreet man who had good judgment. Without doubt, one of best bankers in Spain's history."

JOSEP OLIU, Chairman of Banco Sabadell, in a note:

"(The loss of Botín) is especially significant given that he was the main push behind the national and international development of the first financial group in the euro zone and, right now, one of the ten best banks in the world."

CÁNDIDO MÉNDEZ, head of Spanish union UGT:

"Emilio Botín has been a fundamental protagonist in the internationalisation of the Spanish financial system. Banco Santander is a reference for all financial changes and innovation at a global level.

"He had a very singular management style that probably will never be repeated."

SPANISH BANKING ASSOCIATION:

"Emilio Botín leaves as his legacy a modern banking group with a great international presence and a management team which will guarantee the continuity of Santander as one of the main financial groups in the world."

BANK OF SPAIN:

"With his death, we've lost an exceptional figure from within the international financial system, who always knew how to combine the interests of the bank with the general interests of Spain."

SERGIO ERMOTTI, chief executive of UBS:

"It's a great loss to the industry. He was a pioneer and a friend of UBS. We will remember him for his energy, his sharp mind and good heart. Our sympathy goes out to his family and the employees of Santander."

GEORGE MATHEWSON, former Royal Bank of Scotland chairman, who worked closely with Botín for 25 years. RBS and Santander had a strategic alliance between 1998 and 2004 and Botín and Mathewson sat together on the boards of both banks:

"He had a great capacity for learning and never assumed he knew everything. He was always willing to learn which was a great capacity for a man of his seniority to have. He sat on the RBS board for years and was constantly taking notes and learning about the business.

"He made a major contribution to Spanish banking. He brought discipline to banking in Spain."

(Compiled by Reuters bureaux; editing by Julien Toyer, G Crosse and Mark Potter)