Jerk with a Heart of Gold: His inusfferable genius qualities make him a bit of a jerk, as does his obsession with finding the Book of Leaves and his Mother, but ultimately he wants to do the right thing and will come to his friends aid.
Large Ham: He hams it up when he straps down that magister and threatens to smear his image forever by showing everyone a photo of him fucking a pig. And many other times, such as when he turns down the Vatican's offer with his new guns while putting on a show of his loyalty for Lorenzo.
Missing Mom: He mother's whereabouts have been unknown since his childhood. She was a member of the Sons of Mithras, and the last person known to possess the Book of Leaves.
Sanity Slippage: After Leonardo is arrested, some are convinced he has slowly lost his mind in prison. Even Leo himself wonders that. And given his behavior at the trial...
Sherlock Scan: Animated to look a lot like Leonardo's historical drawings and blueprints.
Played By: Laura Haddock
Action Girl: When it comes down to it, she can usually handle herself.
Foil: To da Vinci. She says herself that the two of them are living proof of his belief that people are capable of anything; he's proof of the heights they can reach, and she's proof of the depths they can sink to.
The Mole: She uses her relationship with Lorenzo as a means to gather information for Rome.
Lorenzo de' Medici
Played By: Elliot Cowan
Authority Equals Asskicking: While not as skilled as his brother, he's shown to be able to more than hold his own when he needs to. Notably, in the season 2 finale, he almost effortlessly disarms Alfonso, who had been one of the only combatants in the series to outmatch Leonardo.
Hot-Blooded: Giuliano 's ghost claims he works best when angry.
Reasonable Authority Figure: Most of the time. When Leonardo's first prototype cannon explodes, he gives him another chance to fix the flaws in the design.
The Resenter: He secretly always resented Giuliano for being better at him in martial pursuits and living a life free of responsibility, and ultimatley, for dying before him.
Revenge Before Reason: When he gets mad enough. When Lorenzo thought Becci betrayed him, he had the man who had taught him as a child and advised him all of his life sentenced to a painful death, despite several others criticizing this and even suggesting that Becci might not have been the spy.
Unstoppable Rage: Combines it with Tranquil Fury; when he's significantly angry, his mind becomes more focused, significantly improving his combat abilities.
Your Cheating Heart: Cheats on his wife frequently; at the start of the series he's having an affair with Lucricia, and she's not his first mistress. Later in season 2, he resumes a romance from his youth with Ippolita, Alfonso's wife.
Giuliano de' Medici
Played By: Tom Bateman
Authority Equals Asskicking: He is both the co-ruler of Florence and very good in a sword fight. He's notably more capable than his brother in combat, and his brother is a badass in his own right.
Back for the Dead: He was set up to look killed, but turned out to be alive, only to actually be killed.
The Charmer: He has this reputation; the Pazzis note that though Lorenzo is the brains of the Medici family and handles the politics, it's Giuliano who's charmed the hearts of Florence's people.
Handsome Lech: He has a well earned reputation as a ladies man, helped by his good looks and the fact that his family rules the city.
Hidden Depths: Originally presented as a small minded, anti-intellectual brute of a man, as the series progresses he's shown to be genuinely charming and caring, protective of his family, to truly believe in Florences' ideals, and to have more cunning than most credit him with.
Jerk with a Heart of Gold: He's rather hostile towards Leonardo as he sees the artist as a social climber, but he genuinely cares for his family and for Florence.
Played By: Gregg Chillin
Ambiguously Brown: His exact race is unknown, as he's very dark for an Italian. He's implied to be a Half Breed, of some sort, and fans usually assume that he is of Arab decent. Or perhaps Persian since Zoroaster is the name of a famous Persian religious figure.
Badass: One of the more capable combatants in the series.
Badass Bookworm: Not quite up to Leonardo's level, but he's one of the few who comes close. He's able to calculate the rate of fire of Leonardo's pipe-organ muskets after watching a single demonstration.
The Heavy: He's the antagonist who the plot for most of the first season.
Heel Face Door Slam: After a traumatic series of experiences in South America, throws himself on the mercy of his uncle, the real Sixtus, begging for either absolution or death. Sixtus grants him neither, refusing to forgive him for standing by while his daughter was slaughtered.
Screw This, I'm Out of Here!: In the season 2 finale, she flees Florence with her children, deep in shame over her affair with the traitor Carlo, and after learning that a massive sum of money was withdrawn from the bank by a member of the Medici family and that she'll now be held accountable.
Silk Hiding Steel: She's a lady, but much more knowledgeable and canny than most would assume.
Your Cheating Heart: Season one drops hints that she has an interest in her brother-in-law, Giuliano, but they never act on it. Season 2 has her begin an affair with Carlo da Medici, her husband's great uncle(who's about his age.)
Rome and Allies
Federico da Montefeltro/Duke of Urbino
Played By: Vincent Riotta
Badass: He's more than a match for Leonardo in combat, only being defeated when da Vinci exploits his lack of depth perception.
Blood Knight: He's very eager to lead his men into combat; he doesn't particularly care who's paying him.
The Brute: He's employed by Rome to act as their muscle.
Combat Pragmatist: Once he lost his eye, he also removed the bridge of his nose so as not to loose his peripheral vision. Unfortunately, he can't do anything about his lack of depth perception.
Even Evil Has Standards: After taking Florence and imprisoning Clarice, he refuses to rape her, stating that he'll only have her if she's willing.
Cain and Abel: He's the evil sibling. His brother, the real Francesco, is the good one.
Evil Twin: To Lucrezia's father, the real Francesco Della Rovere.
Evil Uncle: To Lucrezia. He imprisons her father, who's the real pope, and killed her younger sister right in front of her.
Depraved Bisexual: He first shows up molesting a young man while holding a knife to his throat, though there are later allusions to him having affairs with women as well, with comments by one of the women that he "hurts" her.
Manipulative Bastard: He tries tempting Da Vinci with the Vatican Secret Archives, and claims that the Turk is actually a secret agent of the Ottoman Empire to discourage Da Vinci.
Knight Templar: His ultimate plan is taking Florence and the rest of Italy to wage war against the Ottoman Empire.
Pedophile Priest: The first we see of him, he's naked in his bath with a young boy and a knife on the boy's neck.Subverted in that he isn't actually a member of the clergy at all, he's just impersonating one.
The Usurper: To Francesco, the true Pope Sixtus. He is shown to have initiated a cue, in the second season.
Cain and Abel: His brother had usurped the papacy from him, in addition to attempting to drown him as a child. According to Lucrezia, Alessandro has always resented the fact that Francesco is the firstborn.
The Chess Master: He's shown to be a master of go, and he's playing the long game to gain his freedom and vengeance all in one swoop, passing up opportunities to escape because the time isn't right yet.
Cruel Mercy: When Riario throws himself at his mercy, begging for either absolution or death, he refuses to grant either, forcing Riario to live with the weight of his sins.
Revenge Before Reason: Bizarrely mixed with Cruel Mercy; he refuses to kill Riario when Riario tries to offer his services to the Prisoner as penance, unable to forgive Riario for the role he played in his daughter's death, despite the fact that Riario is perhaps the most valuable pawn he could hope for, but at the same time, he refuses to kill Riario, either.
Smart People Play Chess: He is usually seen to be playing the Chinese game of go, and is shown to be quite capable of strategy.
Shadow Archetype: To the Pope. The similarities in their deception are discussed by Lucrezia and The Turk.