Lord Sinclair was a wealthy noble of Kandarin. He was a good friend of King Ulthas and did many good works for the people of the kingdom. Lord Sinclair and his children lived in a large castle to the east of Seers' Village. His children were spoiled by his wealth and considered themselves even more important than the king.
In the year 132 of the Fifth Age, King Arthur and the Knights of the Round Table came to Gielinor from another world. Once there, they realised they were in need of a castle. King Ulthas, the king of Kandarin at the time, met with Lord Sinclair and discussed King Arthur's plight. Sinclair decided that he would give his castle to King Arthur and relocate himself and his family to a large mansion in the north, near the southern border of the Fremennik Province. He renamed the mansion Sinclair Mansion. King Arthur, meanwhile, renamed the castle Camelot.
Lord Sinclair's children were unhappy with the turn of events, however, and believed that they deserved Camelot more than King Arthur. From that day forward, they held a strong grudge against their father. Many years later, Lord Sinclair was found stabbed to death in the mansion. One of his children was convicted and imprisoned in the courthouse in Seers' Village. It was later revealed, however, that Lord Sinclair's murder was part of a longer chain of events devised by two of his children in order to reclaim Camelot from King Arthur.