Slade is an extremely calm and composed individual, remaining an enigma to both enemies and allies alike throughout the series. As a result, not much is known of his true personality by anyone, although the comparison has been made on multiple occasions by multiple people that he and Robin share similar traits, such as an intense dislike to lose and are fiercely dedicated and, borderline obsessive in accomplishing their goals.

Although many people don't know Slade's intentions to fight, it is made clear a couple times. In Birthmark, Slade quotes that it is, "always the quiet ones", and in Apprentice Part II, he quotes, "Betrayal. Destruction. Revenge." These all may reference his son Jericho, since he can't talk, and the incident leading up to him being unable to talk (and Slade losing his right eye) was because of Slade supposedly betraying his family, which led to the minor destruction of his home (but major destruction to him and his son), which led to Slade wanting to get revenge on unknown people to make it up for his son losing the ability to speak.

The epitome of an evil mastermind, Slade is clever and calculating, never coming into view unless he has the complete advantage, and flees the moment that advantage is compromised. A master manipulator, he prefers to bait others into traps rather than directly confront them himself, and uses his robotic minions to their fullest extent, as they're often seen fighting in his stead. Throughout the first two seasons, for reasons which are not entirely clear, he is shown tirelessly working on recruiting new apprentices, setting his sights on both Robin and Terra respectively. Using his intelligence and charisma, he exploits their weaknesses and fears, and is not above blackmailing them into submission, as he did with Robin in Apprentice Part I.

Slade is scary and intimidating due to his evil and sadistic personality. He is so stubborn and determined on what's right in front of him which becomes his downfall. His stony disposition makes him seem all the more ruthless and unemotional.

In a conversation with Robin in The End Part II, Slade admits to feeling no remorse for any of his crimes, saying "it's what I do best" when Robin tells him that everything that he's ever done has only made people suffer.

Occasionally he will lose his temper. An example is when Trigon betrayed him and had his minions seize him, which lead to him demanding the demons to obey him with outrage.