RIO DE JANEIRO, Aug 29 (Stuart Grudgings/Reuters) - His cartoons are edgy, bold, and a thorn in the side of the Arab world's tottering authoritarians -- a gift to protesters from the unlikely setting of an apartment in beach-side Rio de Janeiro.

Carlos Latuff, a 42-year-old leftist whose only family link to the Middle East is a Lebanese grandfather he never knew, has become a hero of the tumultuous Arab Spring with rapid-fire satirical sketches that have helped inspire the uprisings.

All he has needed is his pen, a passion for the region's struggles and a Twitter account that he uses to send out his cartoons.

Starting with the Tunisia uprisings last December, Latuff's work has been downloaded by protest leaders and splashed on T-shirts and banners at protests from Egypt to Libya and Bahrain, becoming a satirical emblem of outrage.

In one, a jackboot representing Syria's government stamps on a hand writing the word freedom. In another, a man representing justice under Egypt's military rulers holds a scale full of imprisoned protesters.

Latuff said he first knew his cartoons were having an impact when, watching TV, he saw them printed on banners as protests swept Egypt on Jan. 25, only two days after he had made them available.

That gave me certainty that my job was useful, Latuff told Reuters. It's not the social platforms that make revolutions, it's the people. Twitter, Facebook, just like a camera or Molotov cocktails, are just instruments, equipment.

Latuff, who does work for Brazilian newspapers and other outlets, doesn't charge protest leaders for his work, saying he donates the cartoons to highlight injustices and to show his solidarity against authoritarianism globally.

At home, he has been in trouble with authorities several times for hard-hitting images depicting police brutality in Rio's slums.

His only visits to the Middle East came in 1999 and 2009, when he went to the occupied Palestinian territories and later Palestinian refugee camps in Jordan and Lebanon.

MAKING FRIENDS, AND ENEMIES

It was enough, he says, to give him an understanding that the dynamics of oppression in the region were similar to those in Rio's violence-plagued slums, or favelas.

Misery is the same in any country, he said. The only difference was that women covered their heads, the writing was in Arabic, and the men with guns were militants, not drug traffickers.

Latuff's foray into the divisive world of Middle Eastern politics has made him plenty of enemies as well as friends. His uncompromising work depicting Israeli army brutality toward Palestinians -- one cartoon compares soldiers with Nazi Germans -- has drawn allegations that he is anti-Semitic, a charge he strongly denies.

The cartoonist, wearing a Free Palestine badge and War is Business T-shirt, attributed the strong demand for his cartoons among protesters to the continuing lack of freedom for journalists in the region.

Many of his cartoons still focus on Egypt, where emergency powers for the security forces remain in place six months after Hosni Mubarak was toppled. One recent piece shows a snake looming behind a woman sitting at a computer -- a reference to the recent arrest of activist Asmaa Mahfouz for insulting the military in a Twitter comment. The army later acquitted her.

Most people don't know what is happening now in Egypt -- because Mubarak left the government they think they have democracy, but this is not true, Latuff said. (Additional reporting by Julia Aquino; Editing by Kieran Murray)