Robert [de Toeni], called de Stafford; held by 1086 nearly 70 manors in Staffs, more than 25 in Warwicks, more than 20 in Lincs, 10 in Oxon, one in Worcs and one in Northants; built what later became known as Belvoir Castle; allegedly married Avice de Clare, and died probably 1088. [Burke's Peerage]
--------------------------------------------
Even though BP, above states that they are the same person, there is no definite proof either way. One person in soc.genealogy.medieval has speculated that Robert of Belvoir was son of Roger de Toeni by his Spanish 1st wife, while Robert de Stafford was a younger son by his 2nd wife Godheut. It makes sense to me, which is why I have portrayed my pedigree that way.
-------------------------------------------
Amongst the most distinguished companion in arms of the Conqueror was Robert de Todeni, a nobleman of Normandy, upon whom the victorious monarch conferred, with numerous other grants, an estate in the county of Lincoln upon the borders of Leicestershire. Here de Todeni erected a stately castle and, from the fair view it commanded, gave it the designation of Belvoir Castle, and here he established his chief abode. At the time of the General Survey, this powerful personage possessed no less than eighty extensive lordships, viz., two in Yorkshire, one in Essex, four in Suffolk, one in Cambridge, two in Hertfordshire, three in Bucks, four in Gloucestershire, three in Bedfordshire, nine in Northamptonshire, two in Rutland, thirty-two in Lincolnshire, and seventeen in Leicestershire. "of this Robert," saith Dugdale, "I have not seen any other memorial than that the Coucher-Book of Belvoir recordeth: which is, that bearing a venerable esteem to our sometime much celebrated protomartyr, St. Alban, he founded near to his castle a priory for monks and annexed it as a cell to that great abbey in Hertfordshire, formerly erected by the devout King Offa in honour of that most holy man." Robert de Todeni, Lord of Belvoir, d. in 1088, leaving issue by his wife Adela, William, who assumed the surname of Albini; Berenger; Geoffrey; Robert; and Agnes. He was s. by his eldest son, William de Albini, Brito, Lord of Belvoir. [Sir Bernard Burke, Dormant, Abeyant, Forfeited and Extinct Peerages, Burke's Peerage, Ltd., London, England, 1883, p. 160, Daubeney, Barons Daubeney, Earl of Bridgewater]
Note: Robert was father of Adeliza, who married Roger Bigod and had Cecily, who married William de Albini. William did succeed Robert as Lord of Belvoir, but as a grandson-in-law, not as a son as Sir Bernard Burke states in "Dormant & Extinct Peerages" above.