By Alex Kirby BBC News Online correspondent

Rowan Williams, the new archbishop of Canterbury, has never dodged controversy.

But he faces the prospect of entering areas where he may find himself challenging state and church.

No job description for an archbishop of Canterbury exists.

Each new occupant of St Augustine's throne has to make up the job as he goes along.

Dr Rowan Williams, the 104th archbishop, will face the same terrifying freedoms and enervating constraints as his predecessors.

But what he does is likely to be radically different from what the church has learnt to expect of its leaders.

Archbishops are supposed to combine prophetic zeal with managerial acumen.

Dr Williams, described as "so vague he could get lost taking the dog for a walk", is unlikely to rate church management too highly.

Strong convictions

A kinder observer said he inspired awe and affection in equal measure, and he is probably one of fairly few church leaders who is genuinely holy.

Holiness is easier to recognise than to describe.

It combines compassion, simplicity and certainty, and a whole lot more besides, and it respects the absolute right of others to be who they are.

Rowan Williams draws his inspiration from a faith he lives rather than preaches.

The trouble with holy people is that they do not fear to speak and act as they think they should.

Dr George Carey stands down in October

So this will be an archbishop who tells the truth as his faith shows it to him.

One Anglican priest told BBC News Online: "Rowan doesn't care a fig what people think about him."

"And although he cares passionately about individuals, that won't divert him from his convictions.

"He lives his faith like someone who genuinely believes it.

"T S Eliot, in Ash Wednesday, writes: 'Teach us to care, and not to care.' That's Rowan for you."

Within the church the new archbishop will face hostility over his understanding of sexual morality.

He accepts that divorced people can be remarried in church, which the hardliners reject.

Far worse, in their eyes, he accepts that gay and lesbian Christians can be members of the clergy.

Outspoken

This pits him against traditionalists within the church of England itself, and also within the much larger worldwide Anglican communion.

He will be the leader of the world's 70 million Anglicans, not just of the English church.

Dr Williams belongs to the Anglo-Catholic wing of the church, which is usually more socialist than anything else in its politics.

He will want the government of the day to give priority to the poor, in line with his understanding of the Christian gospel.

And he will not be silent over world events.

He talks about Christianity in a way ordinary people can understand

Paul Vallely Independent newspaper

He has criticised the bombing of Afghanistan.

With other church members, he has signed a declaration saying that an attack on Iraq would be "immoral and illegal".

Paul Vallely is associate editor of the Independent newspaper, and knows Rowan Williams well. He told BBC News Online: "Rowan is unpredictable. He doesn't follow a set line.

"People call him a liberal, and in many ways he is. But he's an orthodox liberal when it comes to doctrine.

"And he talks about Christianity in a way ordinary people can understand."

Rowan Williams, like a distant predecessor as archbishop, Thomas a Becket, may prove a turbulent priest.

He may also persuade more of us that the church is not just a comfortable members' only club, but something that exists to change the world.