The founder of the Targeryen Dynasty, Aegon the Conqueror.
Before him Westeros was ruled by Kings, not lords. He also had 3 dragons like Daenerys. He conquered all of the kingdoms in Westeros (minus Dorne) and made himself King of the entire continent.
From his wiki page (if you don’t know much about him):
Aegon I Targaryen, known as Aegon the Conqueror, is an unseen character in Game of Thrones. He died almost three hundred years before the time of the series, and is not expected to appear. Aegon I Targaryen conquered all of Westeros (with the exception of Dorne) with three great dragons, Balerion, Vhagar and Meraxes, and unified the realm under his rule, founding the Targaryen dynasty. He was married to both of his sisters, Visenya and Rhaenys. He is a direct ancestor of Daenerys Targaryen.
EDIT (in response to OP comment):
After the Conquest, Aegon ruled for thirty more years, apparently wisely and well.
He also knew that conquering Westeros had been the easy part and that the hard part would be maintaining the realm he had built. To ensure that his dream would not die, Aegon spent most of his time traveling the various Kingdoms on royal progresses to remind lords and smallfolk who ruled them and to make his presence familiar to them. He also refrained from trying to unite the Kingdoms under the same laws, instead allowing them to retain their old laws and he would judge crimes committed in these Kingdoms according to their customs.
It continues on and on about him. He was just, ruled failyr, was kind to the defeated, didn’t enforce his laws on the conquered, was friendly to the Faith of the Seven (even when that wasn’t his religion) etc. So if anything Dany is very much like her ancestor in many regards.