He should not be confused with Eldacar, the fourth King of Arnor.
His reign saw the already lingering unrest explode, for he was the son of princess Vidumavi, a daughter of the Northmen King Vidugavia, a lesser Man.
After ascending the throne in 1432 T.A. he reigned for five years when he was deposed and driven from Osgiliath into exile to Rhovanion by his far relative Castamir the Usurper in a civil war called the Kin-strife.
In 1447 T.A. he marched south with his army and slew Castamir personally in battle at the Crossings of Erui. But Castamir's sons escaped and Gondor's purest blood was spilt. He besieged Pelargir where Castamir's sons held out the last resistance. Eldacar had no ships at his disposal (for Castamir was the Lord of Ships of Gondor) and Castamir's sons finally fled to Umbar.
Eldacar reigned until 1490 T.A. and was succeeded by his second son Aldamir.
Castamir the Usurper