Hugo Chavez was elected President of Venezuela on 8 December 1998 and took up office in January 1999, so he has been in office now for almost 14 years.
Originally Chavez was a revolutionary activist who never intended to run for President at all, as he believed the electoral system was fundamentally unfair. However, after a number of polls and surveys showed that he was popular enough to win, he finally entered the race and was elected with a large majority.
He was re-elected in 2000 with another large majority, and again in 2006. The election was monitored by outside observers and pronounced fair. In October 2012 he was elected once again, though with a much smaller majority, and would normally serve until the end of 2018. However, he has had serious health problems, and also his popularity is much less than it was, so whether he will complete this term remains to be seen.
You can read a profile of Hugo Chavez here.