Maybe the ex-Sandinista who runs Nigeria?
If you've been following recent events, it's pretty clear he's still an authoritarian at heart – although no longer a communist.
To add on, there have been several in Latin America: Manuel Zelaya, former president of Honduras who was elected on a center-right platform but in less than three years moved a good deal to the left; and Fulgencio Batista of Cuba, who was a relatively popular democratically elected president before becoming a dictator which ultimately led to the Cuban Revolution. In fact, Fidel Castro himself was not fully known to be a communist until well after he had established himself.
There's also F. W. de Klerk, elected as a conservative but who began to oppose and ultimately dismantle apartheid.
And Michael Manley, who served twice as prime minister of Jamaica: the first time, for most of the 1970s, as a democratic socialist, and the second, from 1989 to 1992, as a Third Wayer.
