History:

Manga
He doesn't know his history that much beyond the orphanage. His parents died in a car crash when he was young. Either by head trauma, or by fear, he forgot who his parents were. He is a permanent amnesia case. (Later on too.. he is easily brainwashed)

He grew up in the orphanage and when he was old enough, he got his own apartment and went to highschool. He then met Usagi and commented on her odango! (which made history!)

And he keeps living his former life. He seems to know a lot more than the manga actually gives on him. He seems to also be connected far more to his past life than any other character I've seen in the manga. (Save for maybe Hotaru). Since there are not a lot of his own memories, he only has his past life and the present to live on.

Ironically... you'd think if the present was that precious he wouldn't get brained washed for 4 out of the 5 series. But he does.. I guess it means girls everywhere can dream that they can brain wash him into liking them.

Anime:
The part about his parents was kept. The part about him meeting Usagi in the Sailor Moon R movie however is invented. In fact that movie does not fall in the Sailor Moon timeline. So it might be considered obsolete to the major timeline.

The only thing is that he's been brainwashed a total of 2 times, as supposed to the total of 5 times in the manga. So it's harder to brainwash him in this version. However, his history seems greatly shortened, and he has a shorter history. While it does show him working in various places, such as a hotel, it gives less background history. Since the Silver Millennium is neglected much more in the anime, and he is a character rooted firmly in the past more than of the presents past, it's like he was chopped. The anime makes up for this by stereotyping his character, so people won't notice as much.

PGSM:
It's obvious he was an orphan, but it doesn't go into his past as much other than he has amnesia. He does however have a benefactor who helped to support him.

When he awakens as Prince Endymion he can transform into the Prince and fight- without any super-special powers- with his sword. This version deals with the past more and Mamoru's vow to change fate so that he and Usagi could be together.

He also spends part of the series abroad in London to study, though he is still featured being harassed by Zoisite (T_T) despite being far away from the Princess.

Essentially he is the same Mamoru as the manga, despite the plot differences. He is more of a romantic than the anime version and very devoted to Usagi.

Personality:

Manga:
He is mysterious, kind and has a gentle heart. He won't give up, and most of all he doesn't say corny lines. He is the support for Usagi as much as Usagi is the support for him. H is very intelligent, and has helped the senshi in more than distraction. He has helped somewhat in strategy too. He has his own history that includes the generals. There is more of a sense and a roundedness to Mamoru in the manga than anime.
He doesn't break up the fights between Usagi and Chibiusa as much either (they don't fight that much anyway). He stands by Usagi and when he's needed he's there. He also in the manga, unlike the anime is able to get jealous.
His character for the most part is unknown and no labels can really be stuck to him.

Anime:
His character changed more significantly as the seasons went on. This is quite a shame, because in the manga his mystery is often what makes him a neat character, but in the anime it was solved by stereotyping the character into a classic A blood type: uptight, nervous, and studious. He also became the sounding board for Usagi and Chibiusa. He also does not support Usagi as much and spouts corny lines. This is a shame to do to a classic stereotype of Takeuchi-sensei. ^_^ I actually love Takeuchi-sensei's stereotype of this kind of character, because despite it being a stereotype it has depth to it because of the mystery. When the mystery is taken away, there is no depth left.
So Mamoru did lose something, especially in the SMS-SMSS seasons. (in the seasons after that to matter.)
Oh! Furuya-sama has a very nice baritone to bass voice that is smooth and even. It's perfect for the Japanese Mamoru by the cultural standards. It added to the character.. though I must say that sometimes his expressiveness can be a bit lacking... ^^;;

NA Dub
With all the voice changes you would think that it would change his character a lot, but it didn't that much. Most of the voices, save for the first one were the same, and the voicing was the same. No major lines changed his character that much save for the cut corny lines.. which some people who love the manga Mamoru might say is a plus.. Other than that I don't think the NA version really changed his character that much.

Sera Myu
Depended on who played him. See the Musicals section for more information.

PGSM
The main difference is that Mamoru seems more determined to save the world on his own that he is in the other versions. Mamoru takes on many challenges and sacrifices for Usagi early on. First by protecting her as Tuxedo Kamen, but more so later on when he returns from London to tell her that he wants to prove that they can be together without the world coming to an end. He actually promises that it won't happen, and goes through elaborate lengths to try and prevent it.

Rather than letting his Shittenou be killed at the hands of Beryl, he sacrifices his freedom to the Dark Kingdom. He is never brainwashed like in the other versions, he seems more determined and headstrong, and certainly more sure of himself. Later on he requests to spend a day with Usagi and Beryl allows it, but tells him that if he isn't back she'll not only collect him but take away part of his life as well (it is a bit more complicated but that is the idea). Mamoru agrees to the terms but stays late because a Youma attacks and uses up the majority of the day. He sacrifices bits and pieces of his life for Usagi often while in the Dark Kingdom's grasp. The greatest sacrifice he makes in the series is to seal Metallia away in his body to protect the Earth. This leads to his death, which he knew was inevitable...

He is aware of his past but determined to not let it rule him. He is compassionate and cares more about others than himself, most of all Usagi. He tries his very best to take off any pressures she is feeling, more so than any of the other versions he tries to bear her burden for her.

Why He is So Cool!:
This mysterious guy, who nobody can fully rely on in the beginning (and late to the fights as Usagi is to the Sailor Senshi Meetings) makes grand entrances. Roses may seem weak, but they are enough to distract the enemy and wear them down (As seen with Zoicite and her cut face or in "A Curried Affair" against the Monster of the day). He helps the senshi, gives them hints and never takes the stage completely. He is also the senshi of the earth proven by this quote translated from episode 162 "Prince Endymion, the Earth is your guardian star. Whatever happens to Earth, you will suffer the same fate." said by Helios AND Takeuchi-sensei herself (she also says he represents the sun and who should know better than her.) Takeuchi Naoko-san did note in her Liner Notes that she wished he had a bigger role, but the girls took over (it was also her idea to put him in a tuxedo). This can also be seen in the manga if you get them. A lot of the people out there are unforgiving for him taking over the lime light, but get this it can't be an all girls show.

My Tribute Poem to this Magnificent Character:
Chiba Mamoru/ Darien
seems so normal
parents died
Tuxedo Kamen/Tuxedo Mask
Usagi's Hunk
has tons of pride
King Endymion/ Earth Protector
Usagi's husband of the future
Element Earth, the blue and green sphere
mysterious, unreliable
comes when needed
Serena's crush when Tux at first
and boyfriend later
he wears a black cape
a black hat and white mask
shooting off red roses when he is good
black flying through the air when he is bad
White when spirit
He is the senshi of the Earth
carrying Earth's hope
helping and rescuing those in need