Robert Gru

Robert Gru also known as the Bald Terror is a legendary supervillain and Felonius Gru and Dru Gru's father, and Marlena Gru's ex-husband as well. He was also the adopted paternal grandfather of Margo, Edith and Agnes.

History
Before the events of Despicable Me, Robert was a supervillain that came from a long lineage of them and he himself earned himself a legendary status in the villain world. He divorced with his wife Marlena and made an agreement that either of them died for Gru and Dru’s side. some time after Dru and Felonius were born, taking Dru with him, and refrained from approaching them ever since. He then started his career with a hog farm as his front in Freedonia.

Despite being separated, Robert kept an eye on Felonius and is quite satisfied with his achievements, although he wasn't happy with the aspiring Dru, who does terribly at villainy yet insists on keeping the family tradition alive.

Robert died at an unspecified point of unknown causes and Dru inherited his legacy.

Despicable Me
Robert has only been seen in a picture on the Gru Family Tree.

Despicable Me 3
Dru asks his butler Fritz to invite his brother Felonius Gru, who learns from his mother of his supposedly nonexistent relatives. Later on, Felonius Gru witnessed some of his father's legacy at Dru's mansion.

Appearance
The drawing in the family tree in Gru's House depicts Robert as overweight and upper-class with black hair and a mustache. He also has a strange-looking face and like his son, Gru and his divorced wife, Marlena, a long, pointed nose.

In another portrait of Robert in Dru's mansion, his true appearance reveals that he had an uncanny resemblance between his sons with the exception of a bald spot and shoulder length blond hair.

Trivia

 * Robert's appearance shows that Gru and Dru inherited most of their physical traits from their father, though Gru seems to have inherited his hair color from his mother.
 * Being a character that wasn't developed much upon, Robert had some retcons:
 * In the family tree seen in Gru's house, Robert looks different from Despicable Me than he does from the portrait in Despicable Me 3. In the family tree, he is depicted with short curly black hair, and short sideburns, with a horseshoe mustache. His style of dressing also seems different. In his portrait shown in his villain lair underneath his mansion in Freedonia, he has a bald spot, short, straight blond hair, and short sideburns.
 * Robert is implied to be aware of Gru's achievements all along.