Like most Durlan Skrulls, Reep's personality is a unique mix of generosity and suspicion. Among those considered family or friends, he will give and do all he possibly can; helping each other was how what was left of his people survived the Kree attack on his world. It also lent them a pragmatic streak that could be vicious at times, which he has experienced firsthand. In a general sense, Reep believes charity, equity, and understanding are virtues to live by, lessons learned from his father. In a particular sense, however, he is slow to trust and generally skeptical of the motives of strangers. This tendency to doubt, along with his natural inquisitiveness, makes him a fairly gifted amateur detective, and he's used his shapeshifting abilities to great effect in furthering those skills.
Outwardly, it's easy to misunderstand Reep's personality--he makes a point of being friendly, or at least civil, even in unwelcome company. But he is always watchful, always keen to pick up on any hint that those around him may be harboring a hidden agenda, or in any way other than they claim to be. He is fiercely protective of his adopted sister and father, and when his loyalty is earned he is a fearless and devoted friend. Despite having lived on Earth for much of his life, he finds the Earthmen's fractious civilization unsettling, and their social priorities backward. But the planet has been good to his father, and to him, and so he feels he owes it goodness in return. Even when it's really, really difficult.
Durlan Skrulls are shapeshifters, but their exposure to the Kree mutagenic weapon has granted the survivors even greater ability with their species' natural gifts. Reep can assume the shapes of organic and inorganic forms he has observed. His mass shifting is far more flexible than the Skrull norm, enabling him to adopt shapes much larger and much smaller than would normally be possible--he's been a housefly and a whale shark (don't ask), and a virtual Noah's Ark's-worth of shapes in between. He can mimic people, creatures, and objects down to pore alignment or faint structural defects, and this intuitive eye for detail is extremely useful in identifying other shape-changers, as well as reading body language, in general.
Though capable of assuming virtually any form he encounters, Reep only has a limited ability to assume the abilities of those forms. He can fly in the shape of a bird, or exist underwater indefinitely as a fish, but taking Jean Grey's shape wouldn't make him a telepath, and adopting Hulkling's form wouldn't lend him super-strength.
Reep is a natural detective, and fairly accomplished at ferreting out secrets. He is also a talented singer, having had a great deal of practice entertaining his sister over the years. He lacks his father's keen mind for business, but has made a point of acquainting himself with the rudiments, at least. A lifetime of exposure has made him fairly adept with advanced Skrull technology, though there isn't very much of it to access on Earth, at this point.
Disney musicals, Sherlock Holmes, Netflix, the Discovery Channel, museums, zoos, aquariums, people-watching, discovering new and interesting shapes to imitate.
Born in the aftermath of the Six-Minute Death which decimated the Skrull colony of Durla, Reep's earliest memories are of privation and bare-subsistence survival. Millions had died in the attack, and the Empire had quarantined the planet to prevent the Kree-engineered mutagenic plague from spreading. The survivors scavenged what the could in the ruins of the once-prosperous world, shared as much as they were able with their fellows, and made the difficult choices necessitated by a lack of basic resources. Reep and his twin brother, Liggt, were raised initially by their mother. Their father, Renn, had escaped the planet shortly after the Imperial quarantine was lifted in an effort to find something better for his family. But Zhay Daggle died when the twins were barely hatched, a victim of lingering genetic deterioration. Reep and Liggt were fostered by their mother's sister, Ji, until they were on the cusp of puberty.
At that time, the two Durlan Hatchlings were exiled into the wilderness, with instructions that only one would be allowed to return to what remained of their society. With so little left, the colony could not support two adolescents through to adulthood, and so this was deemed the least inhumane option available by the ruling Elders. Initially, Reep and Liggt were determined to do whatever they needed to in order to survive the blasted wasteland together. After six lunar cycles, however, Reep returned to the colony ruins. Alone. He has never spoken of what became of his sibling, and probably never will.
Not long afterward, Reep, following his father's example, stowed away on one of the infrequent cargo ships which had landed on the planet to trade. Renn had left clues for his family to follow, in the event they also managed to escape Durla, and after two years of hopping from ship to ship and station to station, Reep was able to hijack a small shuttle and set course for a virtually-unknown planet in the Milky Way galaxy called Earth.
There, he was reunited with his long-lost father, and was thrilled to discover his shrinking circle of family had been expanded in the form of Renn Daggle's--now living under the assumed identity of green industrialist RJ Brande--adopted daughter, Lu. It was like gaining three new siblings at once, and, while Reep has a difficult time understanding human prejudice toward their own, that has not prevented him from becoming extremely protective of his new sister(s). He's closest to Neutral Lu, or Lu's combined form, but feels deep affection for all three (even if Purple Lu sometimes drives him to distraction). With his father's help, he assumed the identity of Reese P. Brande, and began acclimating to the peculiar culture of Earth.
The kidnapping of one of his sister's selves threw Reep into a frenzied panic, and he fairly terrorized anyone he thought might even be remotely connected to such a thing in search of clues. He was not thrilled when the remaining Lu's contacted their friend Shinobi Shaw for assistance, but will grudgingly acknowledge that he may have experience with this kind of thing that might prove useful. Meanwhile, Reep continues to leave no stone unturned in the search for his lost sister. While generally kindly disposed towards humans, it's fair to say it would be much better for the kidnappers if the authorities find them before he does.