Turkey's former army chief, Ilker Basbug, the most senior officer in a crowded dock charged with plotting to topple the government, is a decorated career soldier with British and NATO training.

If convicted on Monday, he faces life in prison.

The 70-year-old former general led Turkey's military campaign against the rebel Kurdistan Workers' Party (PKK) for many years, only to find himself accused in his retirement of having led a terrorist group himself.

He is among 275 people on trial on dozens of charges related to efforts to unseat government.

Observers believe he is no hardliner, saying he advocated a moderate approach towards the PKK during his tenure at the head of the military and leans politically towards a centre-left opposition party.

"He's no hawk," Sinan Ulgen, head of the Istanbul Centre for Economics and Foreign Policy Studies, told AFP in a recent interview.

Born in Afyonkarahisar in western Turkey in 1943, Basbug graduated from the military academy in 1962 and infantry school a year later, according to a biography on the NATO website.

He graduated from the War College in 1973 and later worked at the intelligence department at NATO headquarters in Brussels.

Basbug studied at the United Kingdom Army Staff College and NATO Defense College before he was promoted to Brigadier General in 1989, according to a NATO biography.

He became a full general in 2002, and was head of the army before taking overall command in August 2008 of Turkey's 515,000-strong military, a force second only to the United States in the NATO alliance.

He held this position until his retirement two years later.

Basbug was arrested in January 2012 and has been in custody ever since on charges of leading a terrorist group seeking to topple Prime Minister Recep Tayyip Erdogan's government.

"The commander of such an army facing charges of forming and leading an armed organisation is really tragicomic," the former general said in his initial testimony last year.

"I always followed the law and the constitution throughout my tenure."

Observers say Basbug's 2008-2010 tenure as military chief coincided with a perceived cooling of the Kurdish conflict, which flared up again when he left office.

"He has made very constructive comments on the Kurdish question," Ulgen said.

In 2009, for example, Basbug had urged Ankara to make sure that its Kurdish citizens benefit from "equal opportunities" and to strive to change the perception among Kurds that "they are being victimised".

University professor Ahmet Insel, author of two books on the Turkish armed forces, said he does not count Basbug among the hardline generals who in 1997 helped bring down the government of the Islamist Necmettin Erbakan.

"He is a general who tries to keep the Turkish army in the barracks," Insel says.

He added that Basbug was known to lean towards the main opposition Republican People's Party (CHP), although the general has never voiced public support for the party created by Mustafa Kemal Ataturk, the founder of modern Turkey and the embodiment of the secular values the army defends.

Observers say that while a moderate in most matters, Basbug's determination to defend the army against coup allegations had forced him to adopt some extreme positions.

As early as 2007, he spoke out in defence of the first officers to be implicated in an alleged coup plot.

When police found an arms cache buried outside Istanbul, Basbug denied the weapons belonged to the Turkish army, referring to more than 20 light anti-tank weapons found among the haul as "pipes".

"He gave the impression of someone ready to say anything to defend the army," says Insel.

Prosecutors say Basbug and other officers planned to create websites to publish destabilising anti-government propaganda, a charge he denies.

But talk of military conspiracies is not easily dismissed in Turkey. The army has carried out three coups -- in 1960, 1971 and 1980.

The power struggle has hurt the military: the waves of arrests, court rulings and constitutional revisions have curbed the force's influence.

Basbug is married and has two children.