Robert with his wife Marlena
Jeffrey Gru (brother)
Marlena Gru (ex-wife)
Despicable Me (photograph)
Robert Gru is Felonius Gru and Dru Gru's father, Marlena Gru's ex-husband as well, he is also the adopted paternal grandfather of Margo, Edith and Agnes, the father-in law of Lucy Wilde and the son of John Gru.
During the event of the Despicable Me 3, he is revealed to be a legendary supervillain with more success than both Gru and Dru.
Robert has only been seen in a picture on the Gru Family Tree but he never appeared in person during the first film or seen in any of Gru's flashbacks and wasn't even at his son's wedding near the end of the second film, or with him and his wife at the Villain-Con in the film Minions.
Despicable Me 3
He also never tells Gru about the fact that he was a legendary supervillain and he always disappoints at Dru in villainy.
The drawing in the family tree in Gru's House shows that Robert is overweight and an upper-class with black hair and moustache, also has a strange-looking face and like his son, Gru and his ex-wife, Marlena a large or long pointed nose.
In another portrait of Robert's in Dru's mansion, he has a blonde hair, which is same to Dru, of different hairstyle.