Strahd von Zarovich originated on a world of the Prime Material Plane, likely in Faerun. (There appears to be a connection between Barovia and the Misty Forest outside of Daggerford, just south of Waterdeep along the Sword Coast of Faerun.) Strahd was the eldest son and heir apparent of King Barov von Zarovich and Queen Ravenia von Roeyen. He was the older brother of Sturm and Sergei, who was born after Strahd had already left home for a long and grueling campaign as a general in his father's armies. During these campaigns, at one point, Strahd was gravely injured. A nomadic group of travelers, the Vistani, found and cared for the wounded prince. In thanks, Strahd granted the whole of the Vistani people safe passage through his lands, always. Strahd eventually pushed back the enemy forces and set up stations to expand his father's kingdom. This area included a valley nestled in the Balinok Mountains, which he renamed Barovia in honor of his father and had a fortified castle built there to defend the new land, which he named Castle Ravenloft, for his mother. After this, his family was invited to visit the new conquered lands.

Sergei had sworn an oath to the Church to join their order, but met a Barovian woman, Tatyana, with whom he fell in love and so decided to renege on his oath to the Church. Strahd was increasingly bitter than his much younger brother felt at liberty to break his oath and ignore his duty to the family, when Strahd had given up the majority of his life and suffered considerable hardship for king and country. When Strahd finally met Tatyana, his bitterness was compounded, as he fell in love with her as well.

Strahd had dabbled in magical arts from time to time, not able to devote himself to the field enough to become proficient because of his own martial duties. With his brother's marriage to Tatyana looming in the near future, Strahd redoubled his efforts to find some magical solution to his dilemma. His envy and regret for lost youth combined with burgeoning interest in the dark arts was sufficient to attract the attention of the Dark Powers of the Shadowfell. The Dark Powers approached Strahd, offering him a chance to claim everything he had ever wished for: make his brother pay for having the chances he himself had never been offered, avenge Sergei's oathbreaking, and win the heart of the girl Strahd loved. While he initially attempted to resist their offer, a series of events inevitably led him to kill his best friend and interrupt both his brother's wedding and a murderous plot against the royal family. Strahd killed Sergei even as assassins killed the majority of the court and army loyal to Strahd. After Tatyana threw herself from the castle walls in despair, Strahd was granted power beyond imagining, enabling him to destroy those who had betrayed him.

His transformation into one of the undead complete, the Dark Powers claimed their price by moving the entire valley into the Demiplane of Dread, a corner of the Shadowfell, where they could enjoy centuries of entertainment watching Strahd struggle and fail over and over again. Over the centuries, they periodically returned Tatyana's soul to Barovia, reborn into different bodies. Whenever Strahd would attempt to reconnect with her, she would be killed in some terrible way, typically by those closest to her in order to avoid her falling into the clutches of "the Devil Strahd". Over the centuries, Strahd took several consorts to attempt to find some sort of peace with interesting and beautiful individuals that caught his eye, all of whom live in Castle Ravenloft with him.

The current year is 735 by the Barovian calendar. This is a rough estimate of important dates/people who have moved through Strahd's life over the centuries (somewhat altered from official standards to make more sense):

c.235 Patrina Velikovna born to dusk elf community in the valley near the Tergs.
c.305 Strahd is born to King Barov and Queen Ravenia on the Prime Material Plane (likely Faerun).
c.325 Having been martially trained from childhood, Strahd is made general of his father's army to fight off the invading Terg forces; over the next 20 years, he steadily decimates their forces and conquers all their lands.
c.332 Tatyana Federovna of Barovia is born.
c.349 The Tergs have been wiped out, Strahd claims their land (now Barovia) for the von Zarovich family, and moves into the re-named fortress (now Castle Ravenloft) to cement their power in the area.
c.350 Sergei von Zarovich moves to Castle Ravenloft, breaks his oath with the church as he fell in love with Tatyana, and plans to marry her. Strahd also falls in love with her and attempts to win her heart.
c.351 Strahd makes a pact with the Dark Powers to regain his lost youth and triumph over his brother to win the girl he loves; his brother is murdered, he becomes a vampire (45yo), Tatyana kills herself (19yo), and Barovia is moved to the Demiplane of Dread, trapping Strahd in his own personal hell for eternity.
c.382 Marina Kresnova born
c.398 Lady Lovina Wachter helped Strahd defeat Lord Leo Dilisnya, who had attempted to assassinate Strahd.
c.400 Marina Kresnova met and fell in love with Strahd (18yo), then was murdered by her father (who wanted to marry her) and the town priest
c.410 Patrina Velikovna, initially met Strahd while he was wooing Tatyana, and was reunited years later over their mutual interest in the arcane
c.520 Patrina Velikovna was stoned to death by the dusk elves for her relationship with Strahd (285yo)
c.525 Ludmilla Vilisevic born in the village of Barovia
c.545 Olya Ivanova born in the village of Barovia
c.558 Ludmilla Vilisevic met Strahd and was turned in 560 (35yo)
c.574 Olya Ivanova met Strahd at a festival, died of a fever in 575 (30yo)
c.610 Escher Majarra born in Faerun
c.630 Sasha Ivliskova born in Vallaki
c.639 Escher Majarra along with his adventuring party was brought to Barovia, met Strahd whom he intrigued, and was turned (29yo)
c.650 Sasha Ivliskova met Strahd and died of sudden illness before she could be turned (20yo)
c.660 Volenta Popofsky born in Tser Pool Vistani community
c.675 Anastraya Karelova born in Vallaki
c.684 Volenta Popofsky met Strahd and was turned in 685 (25yo)
c.696 Anastraya Karelova met Strahd and was turned in 696 (21yo)
c.713 Ireena Kolyana born in village of Barovia, met Strahd at a young age through her father

Currently, Strahd lives in Castle Ravenloft with his four consorts: Ludmilla, Escher, Volenta, and Anastraya. While he loves all of them in their own way, none of them are the woman that he truly loves and longs to be with -- and they know it. Each understands his or her place, and while they may be civil towards one another, sometimes jealousy and sparks fly between the consorts.

Ludmilla Vilisevic (~200yo) Strahd's first consort, now less of a lover and more a friend who also serves as a "maternal" figure for the others, as well as serving as the "face" of the Castle when Strahd is away.

Escher Majarra (~125yo) brought to Barovia by the mists, an adventuring bard, collector of songs, poems, and stories, while he loves Strahd, his heart has been yearning to wander again for some time, yet he fears being forgotten and discarded.

Volenta Popofsky (~75yo) second in command after Rahadin; young, bratty, and beautiful with cruel streak, she is in charge of controlling the monsters in the castle as well as handling matters about the country in need of a "personal touch".

Anastraya Karelova (~60yo) young woman from Vallaki who set out to obtain her heart's desire: one vampire lord with piercing eyes and chiseled cheekbones, both of which and much, much more she will discuss with everyone she meets at great length.