Lived in a funeral home, had a half brother, the product of a young man name Paul Bearer, in the employ of his father, banging his mother on the kitchen floor.
Taker sets a fire in his home. Both his parents die. Kane was (thought to be) burned to death. Paul Bearer takes Taker (and, secretly, Kane) into his care. At this point, he makes a transition into learning the supernatural dark arts.
He splits with Paul Bearer some time before his debut with the WWF and is found by a man called Brother Love. Seeing an opportunity, he follows him into the employ of Ted DiBiase as part of his team at Survivor Series. His dabbling in the dark arts has made him impervious, and devoid of a soul.
His urn is the source of his power; what it contains has never truly been established. More often than not, it's a horcrux of sorts, and houses his spirit when his physical body is no more. This is why it is the key to bringing him back to the mortal world (see: Yokozuna, Underfaker, Kane in 2004, etc.).
Eventually, his longtime confidante turns on him and reveals that his brother is, in fact, alive. He refuses to believe this until Kane shows up and tombstones him at Badd Blood '97. Where as Undertaker controls spirits and spiritual energy, Kane's powers manifested as pyrokinesis. He refuses to fight his brother until finally making peace with his parents in the afterlife, and returns to vanquish his brother at Wrestlemania 14.
Sometime later, he begins to experience delusions of grandeur. His own control of the darkside begins to 'corrupt' his brain, and he begins forming a cult. Paul Bearer is once again at his side, and while Kane wants to rejoin his brother, Undertaker falsely inducts him before kicking him out. He feuded with Vince McMahon for control of the company so that he could manifest Hell on Earth or something to that effect, with the WWF as his vessel.
After he fails at doing this, he adopted Big Show as his apprentice in being an asshole. It didn't end so well, indicating Taker did a good job.
Undertaker starts to like contemporary commercial rock music, and becomes enamored with motorcycles. He also hurts his dick really, really badly. He also gets really pissed at Vince McMahon, and walks out on an opportunity at competing at the Six Pack Challenge for the WWF Championship. While he is away, he literally sacrifices his powers of the darkside so he can fully embrace his enjoyment of motorbikes. He also finds a butterface named Sara and marries her. Seeing the injustice in the WWF and feeling the itch to bring "judgement', he returns, motorbike and all, to the WWF. He also reconciles with his brother, but Kane's pissed at him for whatever reason, and they fight, and yeah. They're mad at each other on and off, but join forces to become a tag team phenomenon in 2001 to some pretty good success.
Undertaker's ego is bruised sometime in 2002, and his enjoyment of commercial rock is lost for whatever reason. He begins to see a resemblance between the ring and his backyard, and considers anyone in that ring to be trespassing. He starts beating up people because of this. This also somehow gives him the determination to win the WWE title several times. The one guy who finally knocks some sense into him and reminds him that his yard does not, in fact, look like a wrestling ring, is Brock Lesnar.
He gets angry at Vince McMahon again, and plans on burying him alive to vent his frustrations, but Kane, now a psycho once more, and remembering that his brother lost his powers, buries him alive. However, he completely forgot about the whole urn thing, and gets pwned by a now dead-again Undertaker at Wrestlemania. The next few years are more or less him fighting for the title, until his physical body was unable, or unwanting, to compete as much anymore. However, his spirit was consistently drawn to Wrestlemania, and the most important battles, the ones his soul was dependent on, were fought at the grandest stage of them all. Eventually, his soul became defined by The Streak, and it became the last thing he fought for. His mortal form could not hold for much longer, and his soul was edging closer to the afterlife. And it did, for the most part, after Lesnar came back and trounced him again, claiming his Streak as his prize.
Taker was called back from the afterlife at this past Wrestelmania by Bray Wyatt, somewhere between himself as a human, and himself as a Deadman. Where he goes from here is a question mark.