Ah, secrets. Just in case you clicked this link by accident, read no further, there are spoilers here!.

Now that the warning's done with, the secrets. Let's delve a little bit into Pierrot's past, shall we?
Pierrot (birthname Leol) was born to two rather famous people- the king and queen of Monaco, Leonhart XIV and his wife, making him a prince (and the to-be Leonhart XV). His mother tragically died shortly after childbirth- we later find that this was because she overate during pregnancy. When the young prince was a mere baby, his father sent him off to be raised by a commoner couple- a tradition of the royal family. However, the couple who "adopted" Leol were greedy and tried to use him for extortion purposes, taking the money given to them and running with it (They later committed suicide abroad). The baby Leol was left abandoned at a circus, Quedam- the last place the couple had taken him. After that fateful show, the ringmaster, Don, and another clown found Leol crying in the seats. Not having any way of knowing whose he was, they decided to keep and raise him. As for a name.... Don took sudden inspiration from some of the clown's equipment and named him: Pierrot Bonnaz.
Growing up in the circus was a fun and yet trying time for Pierrot. He learned everything about acrobatics, juggling, playing to a crowd and being a clown, yet he was always wondering what had happened to his parents whom, he thought, had abandoned him so cruelly at the circus. He grew into a fine young man, and even through (mainly his own) trouble developed individual special skills (such as his ability to duplicate). Upon visiting Japan with Quedam once, he found his first girlfriend, Meg, who loved and appreciated him for who he was (not just a Quedam clown). When the show left Japan, however, Meg didn't come with him, and it was a difficult separation. Don eventually revealed to Pierrot that he had chosen him as the new ringmaster- Don was going to retire soon. Pierrot, though worried, was exhillarated, and worked very hard. Eventually, Pierrot decided that the circus needed to venture into some dangerous areas and perform, and they did so, but this wouldn't be without a price.
Much later, far into the matches of the Monaco Cup, Pierrot is stabbed in the back by someone from his far past- one of the people from those "dangerous areas". Having lost a lot of blood, Pierrot is rushed to the hospital, but there is bad news- he has a very rare blood type, and it'll be very hard to get a transfusion. The King of Monaco, listening, is intrigued- type Bombay blood? Why, that's a blood type that's fairly common in the royal family...! Figuring it out, the King rushes to the hospital in time to save his son and tell him the truth- but then dies from loss of too much blood. Crestfallen, Pierrot trudges along in his duties as the new (and new-found) King. However, there is one saving grace- in the form of a boy named Azuma Kazuma.
For the finals of the Monaco Cup, Azuma is determined to find a way for Pierrot to meet his parents again- and does even better than that! Eventually, Pierrot's parents (that's right, both his mother and father are completely ressurrected, due to Azuma's bread that behaves like a time machine, allowing Pierrot to save his mother and change the past.

So... that's Pierrot spoilers in a nutshell. A very, very large nutshell. ^_^;