Sengir was the son of a small baron on Dominaria. His father started to learn about black magic, as he intended to become immortal, thus initiating his studies in vampirism, bringing his son with him. The baron also made his son Sengir sleep in a coffin many times, even against his son's will. With the passing of time, the young Sengir realized his father's intentions and started to think he could be a better ruler than the old man.
The young Sengir started to visit the village's cemetery during the night to study necromancy, and it was there that he met a little girl, which became an orphan when her parents died during a rat plague which was summoned by the Baron during his black magic studies. Feeling a great magic potential in the orphan, Sengir taught her the song used by his father to control the rats, asking her to kill the baron in order to free the village from the pest. He couldn't kill his father as he wouldn't inherit the baron title. The girl, who had lost everything she could, finally agreed to the plan, after a long conversation.
Sengir and the girl entered the castle with a swarm of pest rats controlled by the young mage girl. When the girl ordered the rats to attack the baron, he sang the same magic song and repelled them. Confused with the battle of wills, the rats attacked the other prey present on the room, the young Sengir. When the rats slashed the boy's throat, the baron cast a spell to save his son, but he was already dead. Feeling that it was the right moment, the girl ordered the rats once again to devour the baron, and they obeyed, finishing the man. After that, she opened a window to let the sun's light in, and then she heard a scream behind her. Sengir was still alive; however, he was injured by the sun's light and retreated to a dark corner of the room, soon realizing he had become a vampire. The girl healed the wound on Sengir's throat, but she couldn't heal the injuries caused by the sun. Anyway, he praised the girl's magic ability and asked her name. She answered: Ravi. They didn't know it at the time, but they would meet again centuries after that moment. On that day, the young man became Baron Sengir.
Centuries passed, and Baron Sengir was summoned during a duel of planeswalkers in Ulgrotha. The Planeswalker who summoned him was defeated and then fled the plane, leaving the Baron lost in that world. It's important to remember that the ancient planeswalkers could use their magic to summon creatures from a plane to another, they were like gods or players like us, nowadays they still can do that, but not like before, I'll write an article explaining that one day.
Anyway, without means to leave Ulgrotha, Sengir chose to make that plane his new home, and each day the vampire became more and more cruel like this father. He found refuge in the swamps and tried to dominate the local people, exterminating them when he failed to seize control. Then he went to the dwarves' castle, and decided to make it his. Sengir massacred the dwarves, resurrecting them as undead. When the survivors tried to recover the castle, he repelled the attack with his zombies until, on the third attempt, in order to send a clear message to all dwarves, he kidnaped the king's daughter and transformed her into a vampire, charming her to love him like a father and renaming her Irini Sengir. Here we have the first great member of the family. This broke the dwarves' spirits, and they abandoned the castle, swearing vengeance and deciding to keep in secret the existence of a planar portal next to the castle.
However, this didn't stop the baron, as he found a secret passage which lead to the portal. Even though he knew little about that, the vampire knew that a planar portal was a dangerous thing. None of the lackeys he sent through the portal returned, and researching the subterranean city and torturing the dwarf prisoners proved to be useless. He didn't manage to discover where the portal lead to, so Sengir decided that he was only going to enter the portal with an army which he would create with the people of Ulgrotha. Looking for answers through the plane, he reached the Dead Zone where he found a ruined tower and, inside it, a sealed coffin. When he opened the coffin, he freed an old mage woman. They didn't recognize each other, but it was his childhood friend, Ravi. The baron quickly realized the great magical power in the woman, bringing her to his castle and renaming her Grandmother Sengir. She became his black magic teacher, offering long lost knowledge.
Later, the Baron started to send his vampires to attack the citizens of Aysen, not to conquer them, but to spread fear in order to break their will. The baron ordered his servants to kidnap humans of Aysen, including families on a ship that was going from Onella to Kerselin. He made them establish small villages on the swamp of his Dark Barony, where they lived under his influence. Even though he didn't need the short-lived humans for any purpose, dominating them kept him entertained during the long years that passed by, and transforming his dead servants into zombies and vampire warriors made them useful. He created firm and cruel rules: He would kill ten people for every person who tried to run away from the Barony.
Sengir had always been aware of the presence of Serra and Feroz on the plane, and soon the Baron decided to meet them personally. Inviting them to a dinner in his castle, the Baron told the two that, since his invocation centuries before, he considered Ulgrotha his new home, and warned the two not to interfere with his territory. Serra and Feroz didn't agree with him, and started to assist the people of Ulgrotha by teaching them magic spells, fighting arts and artifact creation, so they could in the future fight against the tyranny of the Baron. Sengir didn't like rivals and wanted to find a way of getting rid of the two, but time would show him that he didn't need to do anything to deal with Serra and Feroz (see the article about Serra's story). However, he would find out that there were other rivals in that world.
One of these rivals was Eron, the Relentless, which became the King of Goblins, controlling their mountains. The Baron tried to obtain his support, with no success, so the two made a deal, in which Eron would provide food and supplies which the villagers under the rules of Sengir couldn't obtain by themselves, while Baron Sengir wouldn't take hostile actions against the inhabitants of the Koskun mountains. For that moment, Sengir accepted the deal, as he didn't want to lose resources in that moment, but he knew he would "take care" of Eron later.
Sometime later, he was confronted by a Serra paladin known as Lord Ihsan. He asked the Baron to transform him into a vampire, believing that he could kill Sengir with that power. The Baron saw through the paladin's intentions and, instead of transforming him into a vampire, he made him his loyal servant, Ihsan's Shade. Thanks to Ihsan, the Baron learned that his terror attacks were giving strength and purpose to the people of Aysen, instead of fear, and that they were united for their hate towards Sengir. He then stopped the continuous attacks, in order to see if the citizens of Aysen, without a common enemy, would collapse and turn against each other.
After the death of Feroz and with his venomous words, Sengir convinced Serra to leave Ulgrotha. Without his greatest enemies, Baron Sengir would become the true owner of that world. He has spies in Aysen. His loyal hunter Veldrane of Sengir chases those who oppose him. The thieves Joven and Chandler sell the artifacts they steal for whoever pays the most amount of money, so all magical and valuable artifacts end up on the baron's hands. Even Eron knows that their commercial agreement is frail and that many of his guards are secret servants of Sengir, ready to kill him.
The Baron's great plan goes well. He will wait until Aysen's populace is divided, and then the will eliminate Eron once and for all. When thousands of goblins start to starve, they will go where the food is easily available, Aysen. Many will die, but will live enough to destroy lots of villages and farms of the city. After more years of complete misery, the Baron will reappear, putting the weak leaders of Ulgrotha under his control and offering them a choice: Follow him into a new world where they can do whatever they want, or die in misery. The Sengir family grows and obtains more and more strength, and someday the Baron will learn what lies beyond the portal. Maybe he can dominate more than just Ulgrotha.