Cromwell was able to rise to his unique position of power because he was a man of many skills. He was a skilled politician, with a strong personal power base. He had the foresight, determination and strength of will that carried the parliamentarian cause through the crucial trial and execution of King Charles I and its messy political aftermath.
He was also a very talented military leader, a fact which helped his political career. In a short space of time after joining the army in 1642, he was put in charge of the 'Horse' of the cavalry of the Parliamentary Army, which contributed to Parliamentary success in the first period of civil war in 1642-1646. Then, later on, he helped to create the 'New Model' Army - a centralised fighting force which won Parliament many victories such as at the Battle of Naseby in 1645. By the final phase of civil war in 1650-1, Cromwell had become the Lord General of the Parliamentarian army.
Cromwell was also a very controversial figure. He was hated by royalists for his role in the trial and execution of Charles I. He was also unpopular with many parliamentarians who disliked the 'tyranny' of the army and after realising he could not work with them, Cromwell disbanded the Rump Parliament in 1653. In one sense, he replaced a monarchical regime with a puritanical republic. His ideal of religious toleration, which was probably too advanced for its time, was viewed suspiciously by his contemporaries. And his destructive Scottish and Irish campaigns have blackened his historical reputation as statesmen.
All this makes Cromwell's iconography very interesting. Although Cromwell was not a particularly regal to look at - contemporaries noted his austere features and sober, slightly unkempt clothing - he understood it was important for a ruler to look the part. Charles I had set a very strong precedent for how a monarch should be portrayed, and it is interesting to see how far this style continued under the Commonwealth. And the many images of him, reflect the diverse opinions of him from each side.