How had Pompey come into power?
Pompey had gained his influence on the Roman people through his skills on the battlefield primarily, as well as a skills in politics and his intelligence.
In the beginning, Crassus and Pompey became partners so that with their combined power they could achieve their goals more easily. They noted Caesar's charm and growing influence and invited him so that they could achieve even more success.
10 years previous to the Triumvirate, Pompey had been made consul thanks to his militant success, and he held now a political seat as well. He battled pirates on the Mediterranean and punished King Mithradates of Pontus, annexing his kingdom. Becoming an ally to King Tigranes the Great and conquering enemies. Under Pompey's supervision taxes paid increased.
Pompey worked with the Crassus and Caesar only after the Senate refused to give him and his men a well earned reward, and so with their enemies, Pompey made a deal and won his land and ratification as well as a lovely bride; Julia Caesar, daughter of Julius.
However after Crassus was killed by the Parthians and Julia died during labor the Triumvirate fell apart. The Senate called upon Pompey to rival Julius, and although Caesar had offered to make peace Pompey refused, warring against his old friend and father in law, beginning the Battle of Pharsalus.
In the end it was King Ptolemy XIII Theos Philopator who killed Pompey after he attempted an escape to Egypt, decapitating him and leaving his corpse exposed.