"Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men."
This arose as a quotation by John Emerich Edward Dalberg Acton, first Baron Acton (1834–1902). The historian and moralist, who was otherwise known simply as Lord Acton, expressed this opinion in a letter to Bishop Mandell Creighton in 1887. Phrases.org
Although there is a strong correlation between power and corruption, I think it's a mistake to point to the possession of power as the cause. Power doesn't do the corrupting. Rather, the possession of power removes constraints, allowing man's nature to come to the fore.
This nature is shared by believer and unbeliever alike. Notice the Apostle Paul's description of the human condition.
"For I know that good itself does not dwell in me, that is, in my sinful nature. For I have the desire to do what is good, but I cannot carry it out. For I do not do the good I want to do, but the evil I do not want to do—this I keep on doing. Now if I do what I do not want to do, it is no longer I who do it, but it is sin living in me that does it" (Romans 7:18-20).