Douglas Davenport was initially amoral and somewhat atypical of the stereotype of a mad inventor, willing to break legal and moral boundaries by implanting bionics into children and turning them into living weapons to sell on the black market to the highest bidder. It's only after he begins spending time with the Davenport family, and reaffirming healthier relationships between his children and brother, does Douglas begin showing a more humane and heroic side, proving not to be pure evil after all. Before this reformation, Douglas was uncaring and willing to ruin the life of his big brother and everyone he cared about by manipulating, unbuilding and destroying his life, business and family, all out of a impractical personal vendetta.
In several ways, Douglas' personality is reminiscent to that of Donald's, making his hatred of him somewhat ironic. They are matched in both intelligence and paternal instincts over Adam, Bree and Chase. Likewise, Douglas is quite similar to his brother in both negative traits as well. He is prone to being arrogant and having a glorified ego, boasting about himself and his accomplishments, much to the annoyance of his children. Douglas can also be very childish, his revenge against Donald is similar to that of an overgrown sibling rivalry as they partake in bickering and teasing each another. He was implied to resent Donald for most of his life, and this caused Douglas to have a villainous streak into childhood as he bullied his brother (but also claims that he was bullied as well) and being fired pushed him over the edge of madness and evil.
However, Douglas is not completely completely heartless. He proved multiple times to care about the wellbeing and concern of Adam, Bree and Chase. He saved Chase from an avalanche (but in all fairness attempted to sway him to betray Davenport and the team), grew disgusted at the idea Victor Krane's goal of destroying Adam, Bree and Chase and helping Bree fix her broken bionic chase. He also becomes close friends with Leo Dooley, such as granting him bionics to help heal his broken arm.
Douglas has displayed a paternal affection towards his creations, whether they are human or not. This can be seen between the relationship of Douglas and his son, Marcus, who was in reality an android programmed with human responses and emotions, but they nonetheless had a healthy relationship in most regards even though Marcus could find his father somewhat tiresome at times. Though Donald refused to tell Marcus that one day he would simply burn out due to android's low power, he still addressed himself as his father after Marcus was rebuilt.
Douglas is willing to push the boundaries of science, human nature and even morality to achieve results in his pursuits. This can be seen with his use of bionics and his ability to manipulate or upgrade them further, even within human subjects. Although his original plan was to utilise them as weapons, ever since becoming good he has used his knowledge for more heroic purposes, such as medicinally, by implanting Leo's arm with bionics as without the implants he would not have been able to use it any longer. Douglas is also able to foresee the dangers of bionics used against his life and use technology to temporality immobilise said dangers by creating a confinement cell for Adam, Bree and Chase in his lair, adding a deactivation contingent to Leo's new-founded bionics and creating restraints designed to deactivate bionic indivduals, such as Krane.