Miroku is the lecherous warrior monk member of Inuyasha's party in the anime/manga Inu Yasha.
Name
Miroku ("弥勒") is likely named for Miroku Bosatsu, also known as Maitreya. Maitreya is a future Buddha.
Appearance
Miroku is a young human man with short dark hair. He wears a long purple robe with voluminous black sleeves, and carries a tall, gold-coloured staff called a shakujo.
Miroku's right hand is wrapped in cloth, held in place with prayer beads. The prayer beads contain the air void within his hand, of which more below.
Equipment
Miroku's shakujo is a traditional Buddhist monk's staff. It has an ornate metal head with several loose rings which jangle with movement. This is supposed to announce that the monk approaches, so that the monk can rest easy that any little bugs that get trodden on had fair warning. In Miroku's case, the jangling is more likely to alert gigantic slavering monsters to his presence, but he seems to be enough of a traditionalist that the rings remain. Despite being a mere human, Miroku seems to be able to despatch demons to the netherworld with a swift shakujo blow to the head; the staff may be intrinsically magical or Miroku may be able to put a little magic into it for the purposes of demon slaughtering.
Powers
The demon Naraku cursed Miroku's grandfather with an air void (or "wind tunnel") in his right hand. The curse was passed on to Miroku's father and then to Miroku himself.
Usually the air void remains sealed with prayer beads, but when Miroku removes the beads, the void behaves like a black hole, sucking in all and sundry. Anything that is so consumed is never to be seen again. It is immensely powerful, and Miroku can despatch an entire army of demons in one fell swoop. However, he has only very limited control over it (essentially limited to "stop" and "go") and so must be sure that any allies are out of the danger area before unleashing it.
In physical combat, Miroku is a good fighter, but is essentially limited to hitting things with his staff. His real field of expertise is in the mystical realm. As a trained monk, he has magical powers, like a kind of wizard. He's good at sensing magical energy, and knows a number of spells suitable for various occasions. Many's the time that a demon will mysteriously survive being repeatedly bashed about by Inuyasha and Sango, only to spectacularly disintegrate when Miroku calmly flings some mystical scrawls on a scrap of paper at it.
Weaknesses
While Miroku is generally wise, and exercises good judgement, he has a terrible blind spot regarding attractive women. Or, more usually, soulless monsters from hell masquerading as attractive women. He is absolutely incapable of recognising fakers that even Scooby Doo and the gang would unmask immediately.
If Miroku uses the air void to get rid of poisonous creatures, they can sting him on their way through. This renders the air void useless when Naraku's poison insect posse are in the vicinity, which they frequently are. Naraku is presumably acutely aware of how embarrassing it would be to be destroyed by the air void which he created in the first place.
Miroku's real problem is that the air void will eventually consume him completely. His father and grandfather both suffered this fate.
"Pain is nothing. It is death that concerns me."
Relationships
Miroku would like to have as many relationships as possible. He is an inveterate skirt-chaser. Whenever he meets a pretty woman, he asks if she will bear his children, as a matter of course. His lechery knows no bounds; young girls, older women, demons - anyone attractive is fair game and Miroku will drop everything and make any excuse to spend some quality time with her.
"Excuse me, but would you bear my child?"
Sango is, of course, Miroku's most frequent target. This may be because she is his one true love and that they are destined to be together, or it may be because there's only two women that Miroku sees with any regularity, and the other, Kagome, is taken. Miroku tends to get rebuffed (painfully) by Sango because he interprets the slightest affection from her as an invitation to grope her arse.
"Does a woman lose trust in someone just because her butt is groped?" Motivation
As above; Miroku's primary motivation is chasing girls.
In between chasing girls, he hopes to find and destroy Naraku, in order to cancel the air void curse which will otherwise suck him into a void of unknown horror. Mostly, though, for Miroku, it's about the girls.
Role
It's almost impossible to overstate the power of the air void, but it's so often impractical to use. Air void aside, Miroku can certainly handle himself in combat, but he's not up to Inuyasha or even Sango's strength in raw demon-pulverising.
Miroku is the group's magical expert (think Giles from Buffy), and also, frequently, the voice of reason. He is rarely flustered by anything and is able to assess situations calmly. In stark contrast to Inuyasha, Miroku is expert at being sly, sneaky, dishonest, and generally underhand. However, Miroku would argue that he only ever tells white lies, and is always able to explain why his sneakiness is best for everyone concerned.
Character
Miroku is a very interesting character. At times, he seems to embody the qualities of a good monk; he is wise, calm, honourable and selfless. At other times, he seems to be the very opposite of those things; he foolishly chases after women that are obviously going to turn out to be this week's demon-in-disguise, he steals, he lies. The strange thing is that somehow these characteristics don't seem to contradict each other. He doesn't come across as a confused, poorly characterised creation, as you might expect.
I think the key to Miroku's character is that he really believes himself to be honourable. Even as he is tricking a local lord into giving our heroes a bed for the night, on the pretext that their house is haunted and needs exorcising, he explains that it is better even for the lord that they are well rested, as they will be better equipped to deal with the local demons the next day. He will steal from people, but only from those people that can afford it. He chases after women, but he has the utmost respect for them. He's a loveable rogue that thinks he's a saint.
"We ask for nothing in return, except for a place to stay, some food, and women." | 
