Thomas Zarek
Before the Holocaust
Tom Zarek is a charasmatic, eloquent and ideological political agitator who was incarcerated for destroying a government building on Sagitara. His 20-year incarceration lead him to be onboard the Astral Queen, a FTL-capable prison ship that survived the holocaust. Through means unknown, he managed to become the figurehead for all the incarcerated persons aboard the Astral Queen, and almost managed to take control of the ship through force. (Bastille Day)
Zarek came from Sagitara, a colony known to be mistreated by the other eleven Colonies. Through his experiences on that colony, he became an advocate of freedom from slavery. Zarek became a voice for the disenfranchised and, amongst publishing a book that was virtaully banned throughout the Colonies, actively sought to fight against injustices.
To some he is considered a terrorist and nusiance for his tactics, which included the destruction of a government building that resulted in an unspecified loss of life. He believes in the efficacy of violence as a means of change, going as so far as to go to prison over a "matter of conscience" and his refusal of President Adar's politically motivated conditional pardon. (The condition being that he would publicly apologize and pledge to give up violence as a means of change.)
Even some of his own Sagitarians have an intense dislike of him, including Petty Officer Dualla. Despite this, he became a public figure whose name had weight and almost became legendary, thanks to public opinion. (Bastille Day)
After the Exodus
After nearly averting the Astral Queen commander's desire to euthanise the prisoners (thanks to President Laura Roslin's humanitarian decision), (see: Mini-Series) Zarek apparently plotted to escape captivity. With the water shortage and the discovery of a planet that could replenish the lost water (Water), Commander Adama, Colonel Paul Tigh and President Laura Roslin reluctantly elect to utilize the prisoners as badly needed manpower -- the condition being that they would not be treated as slaves and they would agree of their own volition. (Bastille Day)
It was apparently unknown to the aforementioned three that everyone that Zarek was still alive. After an unsuccessful attempt by Lee Adama to persuade the prisoners to help in the recovery efforts, Zarek's sprung the prisoners' escape plan. The prisoners, under Zarek's command, usurped control of the Astral Queen, and taking her crew and visitors (the Galactica contingent) as prisoners. Zarek then laid out his terms: the resignation of Laura Roslin and her ministers, and the free and open elections for a new president, as he deemed Laura Roslin's occupancy of that position to be illegitimate and illegal.
Unfortunately, Zarek's aims were not highlighted in his demands; he wanted a bloodbath to ensue, believing that all that people understood was violence, and that the bloodbath would destroy any credibility that William Adama and Laura Roslin had.
When the situation deteriorated near the point of catastrophe for all involved, Tom Zarek, who was ready to sacrifice his life for his beliefs, was swayed by Lee Adama's promise that he would uphold the Laws of Colonization and hold open elections for a new president, as well as give the ship over to the prisoners as a show of good faith.
Notes
Tom Zarek is portrayed by actor Richard Hatch, who portrayed the original Apollo in the 1978 Battlestar Galactica series.