I'm sorry, Elan, it's too late for that. It has become clear to me that the only way you will accept your proper role is for me to utterly crush you here and now. So I am going to murder your lowlife girlfriend, burn this ship and everyone on it to ash and chop off your hand. BECAUSE THAT IS HOW THESE THINGS ARE DONE! And when you are off brooding and healing for our inevitable final duel, I want you to remember one thing: That you forced me to do this. Just like Nale did.Tarquin to Elan after breaking Haley's arm.
Initially, much like his adventuring companion Malack, he did not initially seem to be a villain, although it had been previously mentioned in the webcomic that he was Lawful Evil. He also appeared to be an ideal father to Elan, even agreeing to spend the day with him. He also seemed rather averse to killing Nale, although he had murdered three of Malack's vampire spawn and the latter wanted him dead for this action.
However, it eventually became apparent that he was actually sociopathic, and that the lives of others meant very little to him. He in fact was tricking others into doing what he wanted and was gradually conquering the entire Western Continent, along with the other members of his adventuring party. He was in fact the reason that Nale became a mass murderer, as he tried to persuade him into becoming like himself.
Shortly afterwards, it was shown that he had arranged for the deaths of some escaped slaves and was burning them alive, believing that they were rebelling against him and deciding that it would be an excellent present for his son if he arranged the burning slaves in his son's name.
Tarquin was also mentioned to have liquefied the men that had sexually harassed his wife in the past, using them as fertilizer for her garden. Also, he had forced several women to marry him. He also seemingly murdered his ninth wife, as he mentioned that she had passed away due to mysterious circumstances, though it was later revealed that she had actually died due to Vaarsuvius not realizing the magnitude of his/her Familicide spell.
Also, after Enor and Gannji captured Elan, Tarquin forced them to fight to the death with each other, also believing that Elan would want this. After they refused to fight each other, Tarquin instructed his minions to shoot them to death with crossbows. Thankfully, they were saved by Belkar Bitterleaf and Ian Starshine.
Tarquin would go on to join the Linear Guild, looking forward to duelling Roy. Likewise, his partner Malack (who he had persuaded into joining the Linear Guild despite his hatred for Nale) decided to deal with Durkon personally, as he had befriended him during his stay at the Empire Of Blood.
After he found out that Nale had murdered Malack the moment his back was turned, and he refused to participate in his schemes, Tarquin stabbed his son in the heart with his dagger. After his associate Laurin Shattersmith disintegrated Nale to prevent him from ever being resurrected, he is unable to understand why Elan never wanted him dead despite him being his brother, as he had tried to murder him in the past.
A few minutes after Nale's demise, it is revealed that Tarquin had framed Haley's father (Ian Starshine) for murder after he needed to assassinate a lizardman ambassador to prevent him from explaining his plans to the Empress Of Blood, simply because he had decided to disrespect him after he had bailed him out of his gladiatorial arena.
Believing that the Order Of The Stick were inhibiting Elan's potential as a hero, Tarquin ordered his men to kill Belkar Bitterleaf, Durkon, and Roy Greenhilt, assuming that he would be able to recruit more members for another adventuring party and telling him that he should be their leader, stabbing through Elan when he tried to use himself as a human shield to protect Roy, telling him that he would survive.
Finally, after Elan summoned Julio Scoundrel to protect him from Tarquin (who turned out to be an enemy of his) and fled from him on The Mechane (Julio Scoundrel's airship), Tarquin immediately told him that he was going to murder the other members of the Order Of The Stick (including Haley Starshine, his girlfriend), murder the Mechane's entire crew, burn the airship to ash, and cut off his hand, believing that he had forced him to do so (as he also believed was the case of Nale).
Tarquin eventually fell over the Mechane once Vaarsuvius pushed him off after Elan refused to let him back onboard, realizing that like his brother, he was too far gone for redemption. Tarquin survived the fall but was left in the desert, pathetically begging Elan to come back and give the plotline a satisfying resolution.
Tarquin was shown to be a very influential and powerful fighter, able to take on the entire Order Of The Stick on his own (with the exception of Vaarsuvius). He was able to use many different weapons, including a knife and a whip. He could also toss Durkon Thundershield by the beard and easily break Haley's arm with his bare hands.
His armor was enchanted, which allowed him to change its appearance at any time. Though his son considered it a weak ability, he was able to save money by doing so during his manipulations.
He was also able to catch Haley's arrows out of the air.