Observers wonder at how a moderate conservative, upper middle-class economist came to court the wrath of Spain by trying to break its richest region away from it.
A hero to some Catalan nationalists and a shyster to their opponents, Mas was described by centre-right Spanish newspaper El Mundo as "the technocrat who turned into the Catalan Odysseus."
With his spectacles and neatly brushed quiff, the 59-year-old father of three started out as a businessman and then served in the regional government before being elected its president in 2010.
He has said that as a youth he was not linked to Catalan nationalism.
But after his separatist alliance and another pro-independence group won an absolute majority of seats in the Catalan parliament in a regional election on Sunday he bellowed: "We have won".
"To some he is an example of loyalty to his homeland and to others he is someone who will lead it to disaster," said Jordi Amat, a writer specialising in Catalan nationalism.
"How did a man seen as a technocrat turn into a patriotic leader?"
Technocrat turns leader
Amat said the "turning point" for Mas was in 2006 when he negotiated political deals including a new statute recognising Catalonia as a "nation".
The agreements with Spanish leaders ultimately fell through and the feeling of betrayal hardened Mas's nationalism.
"That was when the technocrat really became a nationalist leader," Amat said.
Carefully measuring his words in fluent Catalan, Spanish, French and English, Mas trod a cautious line at first as president, trying to negotiate more fiscal autonomy for the northeastern region.
But in September 2012, at the height of Spain's economic crisis, more than a million Catalans filled the streets of Barcelona demanding the right to self-determination.
"I understood that the people were on the march demanding for the first time loud and clear that the right to decide and to be a new state within Europe be made a reality," he was quoted as saying in an interview by the author Teresa Pous.
For months he nevertheless avoided using the word "independence." It was not until 2013, after Madrid had rejected his fiscal demands, that he first publicly said he would vote for secession.
He initially wanted a referendum on independence but shifted tack in the face of legal challenges from Madrid
Mas then called Sunday's early vote for the regional parliament which he framed as an indirect independence ballot. He ran in an alliance with left-wing nationalists and other pro-independence groups.
Branded a 'swindler'
Left-wing critics despise Mas for passing tough spending cuts in the region during Spain's recession.
Opponents also point to recent corruption investigations against his CDC party.
They brand him a liar and a populist.
"Mas is swindling the Catalan people," said the leader of Spain's main opposition Socialist Party, Pedro Sanchez.
"The world is connected and Artur Mas wants to disconnect us," said Albert Rivera, the Catalan leader of the centre-right party Ciudadanos.
Whatever his motives, Mas has pinned his political fortunes to the independence bid in Sunday's vote.
He said before the election that if his side won the election, Catalonia will declare independence by 2017 -- a move Madrid warns is illegal.
"Once this political process is over, I have no great desire to continue my political career," Mas told AFP in an interview this week.
"It is not my ambition to be the first president of the Catalan state. I want to be the last president of the Catalan region."
By Roland Lloyd Parry