There were two routes to sainthood back in the day:
1. Being extremely miserable, usually by depriving yourself of nice things like money, food and sex. Then you deprive yourself of something even nicer, "not being stabbed to death", by going and poking people who are doing just fine without your religion until they murder you for some peace and quiet. You are then beatified as a consolation for the lack of proper psychological help available to you in life. There are many words for people who shout about how everyone must obey their invisible friend, and if you're Christian then "Saint" is one of them.
2. Convert enough pagans and win a free sainthood!
The latter was the choice of Saint Vladimir I of Kiev, because a man with 800 concubines didn't know the meaning of the phrase "self-denial", even if it had been translated into Russian and spelled out with the naked bodies of his octohectomistresses.
Vladimir's path in life was set by his father, Sviatoslav, who divided his kingdom among his three sons - two proper sons, Yaropolk and Oleg, and an embarrassing mishap with a housekeeper, Vladimir (so the title of this piece is entirely factual). This proves that it's possible to have control of an entire country and still not remotely understand what being in power does to people, as war broke out between the brothers approximately four nanoseconds after the father's death. With Yaropolk kicking ass and taking names (specifically, Oleg's) Vladimir bailed to Norway to pick up an army of Vikings and returned in force. And as people with an army of Vikings are wont to do, he won.
Along the way young Vladimirs thoughts turned to love and he pursued Princess Rogneda, daughter of Prince of Rogvolod. Alas, she spurned his love for he was the son of a commoner - but in true romantic movie fashion he used his commoner skills in unexpected ways to work hard and win her heart. And by "commoner skills" we of course mean of course "attack her city and kill her father", and by "win her heart" we mean "sleep with her in the exact opposite extreme of winning her heart, anything saintly, or even basic civilised human behaviour".
Eight years later he decided that boning one princess (and four score times ten spares) wasn't doing it for him anymore and set off after the Greek princess Anna, sister of Emperor Basil II of the Byzantine emperor himself. Scoring with the royalty of a foreign country might sound tricky to you, but no problem for Vladimir "Master of Romance" Svyatoslavich. His heartfelt missive to the emperor imploring the affections of Anna can be shortened to "Yo Basil, I like your sister. PS The citizens of your city of Kherson are dying of thirst, I'm not saying I know anything about the army that's causing that, but they're awful close to your capital city. Okay, bye!"
Basil insisted that Vladimir would have to convert to Christianity first, which was taken as a major victory for The Lord by those on the Greek side, but given that Vladimir already had a conquering army in the vicinity you get the feeling that Vladimir agreed in a shrugging "Fine, sure, whatever" kind of way. For a dowry he killed the rebel uprising against Basil led by Bardas Phocas, possibly the only way mass murder can be an acceptable gift to your fiances family. Then again, however you deliver mass murder as a gift to anyone they're highly unlikely to voice objections directly to the mass murderer.
After that he "put away" his three-quarters of a thousand plus fifty concubines, which in terms of historical euphemisms is right up there with "cleanse" and "relocate". Even those saintly histories that bother to mention that Saint Vladimir, Paragon of Holiness, could have had a threesome a night for a year and never repeated himself don't inquire as to how exactly an entire village of women who now constitute physical evidence of the sins of a public official were dealt with. One would not imagine that pension schemes were involved.
With his new wife he set out to claim his "save a million pagan souls for a free sainthood" bonus prize, presumably because airmiles were not yet available, and did so with the thoughtful New Testament-style strategy of destroying all the statues of the old gods and ordering people to convert. Realising that their king had solved every problem in his life to date with the liberal application of "murdering army", they did.
Around this point he calmed down (by turn of the millenium ruler standards) and stopped declaring war on countries that had made the aggressive move of sharing a border with him. Possibly bored with killing people in foreign countries, he started a civil war within his own. Displaying a lack of pattern recognition that would make a man wheelchairing his way back onto a minefield look like Sherlock Holmes, he divided power over his kingdom among his twelve sons. Apparently having utterly forgotten the first twenty years of his own life. This ended about as well as you can expect, with Saint Vladimir (Conquerer, Rapist, Polygamist and Defiler of Temples) dying en route to killing on of his own children.