The pair returned from Libya in 1989 as part of a 200-strong group dubbed the Special Forces Commandos - the military vanguard of Taylor's National Patriotic Front of Liberia (NPFL) - and started a civil war.
There followed eight years of conflict - in which 250,000 people have reportedly been killed - alternating with failed peace deals, until 1997. That year, Taylor was elected president after threatening to restart the fighting.
During the first three years of Taylor's reign, Blah returned to Libya as Liberian ambassador, before coming home in 2000 to become a low-key vice president, driving his own car around Monrovia with a single bodyguard.
Rebels threaten new regime
Now the 56-year-old former animal-feed plant operator and father of 14 is due to be sworn in as president on Monday, when Taylor has said he will at last bow to international pressure and step down.
Blah will take theoretical charge of an embattled government that holds only around a fifth of Liberian territory, and only part of its own capital, which has been trapped in a rebel choke-hold for two months. It is also not clear how long his government will last.
Peace talks between the regime and the two rebel movements that control much of the country and designed to lead to a new national unity government are under way in the Ghanaian capital Accra.
Commanders of the rebel Liberians United for Reconciliation and Democracy (LURD) say they will accept the results of the Ghana talks, but also that they oppose Blah and will relaunch fighting if a more neutral civilian is not found to replace him.
Thrust into the centre of this political and military storm, Blah remains an enigma to most outside observers. His curriculum vitae has all the hallmarks of a dyed-in-the-wool Taylor clone.
Like his current boss, he is a graduate of Libya's Tajura Military Training College - whose alumni also include Sierra Leone's notoriously brutal rebel chieftain Foday Sankoh - and studied there from 1985 to 1989.
He returned to Liberia in December 1989 as one of the leaders of the NPFL and was the movement's adjutant general until 1990 when he became inspector general and Taylor's envoy to an attempted national reconciliation government.
His posting to Libya was a key one. Colonel Muammar Qadhafi has long been reported to have been one of Taylor's key backers in his years of guerrilla war and brutal rule.
Rift with Taylor
Blah speaks Arabic - along with English, French and his native Dan - and his role must have been an important one as Taylor attempted to shore his regime against LURD's revolution, now almost five years old.
But in recent months there have been signs that the former comrades in arms might not be so close as might have been imagined.
In June, when Taylor was forced to flee a conference of west African leaders in Ghana to avoid an international arrest warrant issued by the UN-mandated war crimes court in Sierra Leone, he accused Blah of plotting to overthrow him.
The vice president was held under house arrest for several days, before leaders from the pair's home region of Nimba prevailed upon Taylor to let him go. The truth behind the allegations remains a mystery, however.