Maussollos (Mausolus) was the Persian satrap and king of Caria (Karia) in southwest Anatolia (modern day Turkey) and a descendant of the Hekatomnid dynasty. He was the son of Hecatomnos and had two brothers, Idrieus and Pixodarus, and two sisters, Artemisia II and Ada. He began his rule in 377 upon the death of his father.
One of Maussollos' first actions upon assuming the throne was to move Caria's capital from Mylasa (Milas), in the interior, to Halicarnassus on the coast. King Maussollos planned to transform his small state into a seat of power culturally, economically, and politically.
In 362 BC, Maussollos joined in a revolt of all the satraps of Anatolia. They planned to break completely free from the Persian king, Artaxerxes II. The revolt suffered setbacks and Maussollos extricated himself from the rebellion before he was brought down along with his allies. From then on, the Persians were so occupied with the unrest that Maussollos was practically autonomous. He was able to spread his rule to Lycia in the southeast and to several Ionian Greek cities to the northwest.
During the Social War of 357-355, Maussollos backed the nearby islands of Rhodes, Cos, and Chios in their battles against Athens. Upon their victory, he was able to use the influence gained to add Rhodes and Cos to his kingdom.
It was said that he was a lover of Helenistic art and brought numerous famous Greek artists and architects to Caria to renovate its cities. Maussollos began the planning of his own tomb before his death in 353 (or 352) and gave the plans to his wife and sister, Artemisia II, who became queen after his death. After its construction, his body was laid to rest in the Mausoleum at Halicarnassus, one of the Seven Wonders of the Ancient World.
A pair of statues from his tomb reside in the British Museum. It was thought that these were of him and his wife but there is a strong chance that they may be of two other ruling class nobles.
Primary source: Encyclopedia Britannica, 2002
http://www.focusmm.com/civcty/caria_00.htm
Note: The word mausoleum is from his name.