It is not known when Robert was born, but it stands to reason it would have to be sometime in the 1920s for him to have fought in WWII.
Robert was a Tuskegee Airman and flew a P-51 Mustang, and was an active participant in the U.S. civil rights movement. During the war, his wingman, Moe, often took credit for things that Robert did or that they dually accomplished together, and Robert's angst about this culminated at Moe's funeral, during which he blows the lid off of some of Moe's more embellished accomplishments. He had close relationship with his sister Cookie. Cookie was the smarter and more responsible of the siblings and often called Robert her "Favorite Dumb Ass."
Robert also lived in Alabama during the U.S. civil rights movement. He specifically recalled showing up late for a march because he forgot his raincoat, much to the indignation of his cohorts. He also had a grudge against Rosa Parks for "stealing his thunder", as he was sitting next to her on the bus and likewise refused to give up his seat. The bus driver was only offended by Rosa's, not his, unwillingness to move, however; also, he claims Malcolm X died owing him five dollars. Robert has three different looks as a young man throughout the series.
While living in Alabama during Jim Crow law, Robert was an accidental and unwilling participant in The Freedom Rides. Robert was trying to skip town back home to Chicago but got on the wrong bus with the Freedom Riders. The Aftermath of the horrifically dangerous ordeal was Robert doing some jail time with the Freedom Riders leader, Sturdy Harris, Who was of questionable sanity.
Robert's exact age is unknown. But for him to be present during World War II and several civil rights events, he would be 90 to 110 years old today (taking into account his cartoonish antics, his relative stamina and energy versus others his age, and the minimum age of World War II participants - at least 86 per 1945 participation). He obviously was married and fathered a son. The exact fates of his wife, son, and daughter-in-law are unknown but they are considered deceased by all accounts. In the episodeRiley Wuz Here, Riley spray-paints a mural on the side of their house of Grandad and his deceased wife on their wedding day, copying a photo from the family album. After Granddad sheds a tear, he thanks Riley and takes a picture of the mural on his digital camera. He then forces Riley to paint over the side of the house.
Robert's combat style focuses primarily on his belt. Because of his experience raising a child (Huey and Riley's father) and then raising Huey and Riley he knows when to use a belt, how to use a belt, and whom to use a belt on. Robert wields his belt in the style of a whip. Robert is shown to use this belt for whupping (normally Riley), restraining (even with no experience he can latch it on people's legs or arms), and offense during a fight. (SeeGranddad's Whip). Even at a young age, Robert was skilled enough to beat several men down with his belt.
He also uses his cane to fight, also similar to the fighting style of tonfa.
During the episode Stinkmeaner: Begun the Clone War Has, Grandad undergoes extreme training and becomes skilled enough in H2H combat to nearly kill the enhanced Stinkmeaner clone.
The best way to describe Robert is that he is old yet unwise. He never accepts responsibility for his actions, nor does he learn any lessons.
Robert has been shown to be extremely prideful, impatient and intolerant. He believes in strict discipline, quick to go for his belt when the boys step out of line. As he says "I hate to see a child go unbeaten." He is not exactly the best father figure or influence. He is perfectly fine with sneaking into movies without paying. A dream sequence revealed that he is cowardly and quick to abandon friends and family to save himself.
Robert describes himself as a "Civil Rights Legend." When describing his experiences during those times he shamelessly includes himself alongside several important figures during that period. Quite frankly he earned more animosity from Blacks then he did White people. He also says he's related to Jackie Robinson. According to him the Freeman is silent.
Robert (aka Mr. Bitches) is also a pathological and compulsive liar; Robert is also quite a womanizer with an extremely unhealthy attraction for women significantly younger than he is.
Robert can also be swayed quite easily by T.V. Advertisments which led to Him purchasing the demonic Siri.
Robert has also been revealed to be extremely incompetent with money and finances. This has lead to him being in debt for two million dollars.
That isn't to say that Grandad is all bad, he has been shown to care for and love Riley and Huey, albeit, he does tend to get embarrassed by their actions or get distracted by other things. He is also shown to have loved his deceased wife, and was touched when Riley painted her on the house.