Per L&M Companion:
(1641 - 1704) A courtier, and said to be the handsomest man in the kingdom, Pepys has stories of his amorous exploits. At first a servant of the Duke of York, he attached himself to the interests of William of Orange after 1679, and commanded the English Regiment in the Dutch army 1681 - 5. He was one of the seven who in 1688 signed the invitation to William to invade England. After the Revolution he was rewarded with a viscountcy, an earldom and high office.
( http://en.wikipedia.org/wiki/Henry_Sydney,_1st_Earl_of_Romney )
Second son of the 2nd. Earl of Leicester, of Penshurst (d. 1677).
( http://en.wikipedia.org/wiki/Robert_Sidney,_2nd_Earl_of_Leicester )
The brother of Algernon ( http://www.pepysdiary.com/encyclopedia/6041/ ) and Robert
( http://www.pepysdiary.com/encyclopedia/9768/ )
Chart showing the number of references in each month of the diary’s entries.