Cedric is the father of Valanice, Queen of Daventry, and husband of Coignice, the miller's daughter, and is a prince of Kolyma.
Background
He was a prince of the fair and tropic land of Kolyma (and possibly later king).[1] He is from eastern Kolyma, an area about which little is known, and is a prince of his land. He and his family live in a castle there.[2] He is married to Coignice. They allowed their daughter Valanice to be educated. It is unknown if that is unusual or not in the land of Kolyma. He made sure she was trained in all the social graces.[3] He made sure she was well taken care of by Matilda. That is all that is known about him.[4]
His daughter was later kidnapped from his household by the jealous crone Hagatha.
The king
There once was a miller who had a beautiful daughter--a daughter so beautiful that he pridefully thought she should be the bride for the king. One day the miller was delivering flour to the castle and, noticing the king nearby, began to to boast about his daughter. The king listened politely, but everyone tells kings that their daughters are the fairest in the universe. "Ah," invented the miller, "but my daughter can spin straw into gold!" Now this got the monarch's attention, and he commanded that the girl be brought to him.
The next day the king put the poor girl in a large room full of straw and commanded her to turn it to gold. The miller's daughter didn't know what he was talking about, for her father had not told her of his lie. Angry, the king threatened her, telling her that she had till dawn to change the straw or she would be killed. With the help of Rumplestiltskin who traded for her necklace, he turned the straw into gold. The king was astonished, but demanded more proof of her skill. He took her to a larger room and filled it with straw, promising the same punishment if she failed. Again the little man came; this time he accepted her ring for the service and again left.
When the king saw all the gold the next day, his heart did not soften towards her; instead, he filled his largest hall with straw and demanded one last magical transformation. If she succeeded, she would become his queen. This time, she had nothing to give the little man, so he demanded she give him her firstborn child in return for saving her life. She agreed, but planned never to have a child. But later a child she had, and had to figure out the man's name in order to keep it.
Behind the Scenes
Cedric is described as 'a prince' of Kolyma. This would suggest he is one of several princes of the land. In fact Count Dracula is a 'prince' of Kolyma, known as the Prince of the Night/Vampire Prince.
Kingdom of Sorrow and See No Weevil both indirectly reference Cedric by mentioning that Valanice is the daughter of royalty on one side. The noble birth raised her station above Graham's.
He is said to be married to a miller's daughter, this may make him the king in the Tale of Rumplestiltskin, and Valanice the child that Rumplestiltskin was trying to kidnap.
Cedric and Coignice are spoken of in present tense in the King's Quest Companion 1st and 2nd Edition which suggests they are both alive at the time of at least KQ5. A second reference to them that appears in the KQ4 chapter also suggests that they are still alive (at least up to the point of KQ4), and appears in all four editions (which includes material up to KQ7).
In the KQC, Cedric is known simply as Cedric. He is not specifically described as Prince Cedric, or Cedric of Kolyma, but said to be a prince, and from Kolyma. The title of this page is for disambiguation purposes, but inspired by Valanice's title "Valanice of Kolyma" (who was also a Princess of that land).
It's worth noting that the Companion states that he is the prince of the "land of Kolyma" which would suggest he is the prince of "western Kolyma" but was originally from "eastern Kolyma". A castle the one he would have had to have lived in is discussed in Kingdom of Sorrow, however the location of that castle is not specified.
As Valanice was a princess rather than a duchess (see Prince of Chouen and Aspen), it can be assumed Cedric was the main line of royalty in the kingdom the next successor to become become king.