Where does the Old Firm derby get its name and how Celtic and Rangers went from friends to foes

The first Old Firm clash of the season will grip Glasgow this weekend as Celtic travel to Ibrox to face Rangers in the Scottish Premiership.

Sunday's meeting will see Brendan Rodgers' side look to come back from May's 3-0 loss, which came after seven games unbeaten in the derby for the Bhoys. Meanwhile, Michael Beale and his men will look to prevent that and move above the Hoops in the table at this early stage of the campaign.

Ahead of the match, here's all you need to know about the history of the Old Firm and why it is so called.

Why is the Glasgow derby called the Old Firm?

The origin of the Old Firm name is not set in stone but is widely accepted to have come from a time when Celtic and Rangers shared a more friendly than competitive relationship.

A magazine called The Scottish Referee published a cartoon in 1904 when the two sides met in a Scottish Cup Final which portrayed a weary-looking man holding a sign that read 'Patronise The Old Firm'.

It's thought that this referenced the rivalry between Rangers and Celtic being invented in order to draw bigger crowds and make more money. In those days the sectarian divide had not reached the level it would go on to in the future.

An alternative belief behind the Old Firm name is that it came from a book published by Bill Murray on the derby. In The Old Firm: sectarianism, sport and society in Scotland, the author referred to Celtic and Rangers as 'like two old, firm friends'.

When did the Old Firm derby become the fierce rivalry it is today?

The Celtic and Rangers rivalry grew as the divide in views regarding religion, identity and politics became more intense in Glasgow.

The Telegraph dates a turning point in tensions to have come in 1912 when Belfast company Harland & Wolff opened a shipyard in Govan.

Traditionally, Rangers fans align themselves as native Scots and protestant with Celtic fans historically being Irish-Scots and catholic.

Before Graeme Souness signed ex-Celtic forward Mo Johnston for Rangers in 1989, the club had gone decades without a Catholic player.

Players and managers over the years have likened the rivalry to El Classico in Spain but many agree it is the fiercest derby of them all. Celtic legend Henrik Larsson labelled it the 'best atmosphere' he had ever played in and Rangers legend Brian Laudrup believed the clash to be 'terrifying'.

Why do some Celtic fans claim the Old Firm derby doesn't exist?

Some Celtic supporters believe the Old Firm derby died in 2012 following the financial collapse at Rangers. Money troubles led the club to be run by new ownership than it had in yesteryear.

As a result, some Bhoys fans prefer to call the fixture the Glasgow derby rather than the Old Firm derby. These Celtic fans are known to refer to Rangers as 'Sevco', the original name of the post-2012 holding company, and rival supporters as 'zombies'.