Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Heir | Status | Relationship to Monarch | Became heir | Reason | Ceased to be heir | Monarch |
| --- | --- | --- | --- | --- | --- | --- |
| Robert Curthose | Heir presumptive | Son | 1066 | father became king | 1077 | William I |
| Succession unclear 1077-1087 | Succession unclear 1077-1087 | Succession unclear 1077-1087 | Succession unclear 1077-1087 | Succession unclear 1077-1087 | Succession unclear 1077-1087 | William I |
| Robert Curthose | Heir presumptive | Elder brother | 1087 | By agreement | 1088 | William II |
| Henry Beauclerc | Heir presumptive | Younger brother | 1088 | Robert's rebellion | 2 August 1100 | William II |
| Succession unclear 1100-1103 | Succession unclear 1100-1103 | Succession unclear 1100-1103 | Succession unclear 1100-1103 | Succession unclear 1100-1103 | Succession unclear 1100-1103 | Henry I |
| William Adelin | Heir apparent | Only son | 1103 | born | 25 November 1120 | Henry I |
| Empress Matilda | Heiress presumptive | Only child | 25 November 1120 proclaimed 1127 | brother died | 1 December 1135 (22 December 1135) | Henry I |
Question:
Who is the Monarch whose Heir is Robert Curthose when the Reason is that the father became king?
Answer:
William I