Afghan Vice President Mohammed Fahim, second from right, attends the last day of the Loya Jirga in Kabul on Nov. 24, 2013. (Omar Sobhani/ Reuters) (Omar Sobhani/Reuters)

Afghanistan’s first vice president, Marshal Mohammed Fahim, a polarizing leader whose political and military career spanned the anti-Soviet war and the American invasion, died Sunday. He was 57.

He died of an undisclosed illness, according to Afghanistan’s presidential palace.

Mr. Fahim’s death leaves Afghanistan without one of its most controversial figures, a man who was expected to play an influential role in the country’s security establishment and its complicated ethnic politics after the American military withdrawal this year.

Born in 1957, Mr. Fahim first gained notoriety as a young commander during the Soviet occupation of the 1980s and then as an anti-Taliban leader in the 1990s — a legacy he would parlay into a formal position of power under President Hamid Karzai. In 2001, with American support, he helped topple the Taliban as leader of the Northern Alliance.

Karzai on Sunday called Mr. Fahim’s death “a huge loss for Afghanistan.”

Afghan Vice President Mohammed Fahim first gained notoriety as a young commander during the Soviet occupation of the 1980s and then as an anti-Taliban leader in the 1990s. (Shah Marai/Agence France-Presse via Getty Images)

While Mr. Fahim’s battlefield experience inspired respect in many, to others he symbolized a new generation of Afghan warlords who profited immensely from his proximity to power and foreign aid. By many accounts, Mr. Fahim grew enormously wealthy in the years after 2002, first during his stint as defense minister and then as vice president.

As he ascended the country’s political ranks, Afghans and foreign diplomats alike grumbled that they were empowering a man with a shadowy record. But many recognized that plucking Mr. Fahim from power would do more harm than good, potentially upsetting a delicate ethnic balance.

In 2002, when aid began flowing to help create a new Afghan army, Mr. Fahim was thought to be one of the main beneficiaries. He was long plagued by allegations of drug trafficking and corruption, which many say helped enrich a growing circle of devotees, mostly from his own Tajik ethnicity.

He built large homes and held private games of Buzkashi, where men on horseback fight for control of goat carcass. He maintained an enormous security detail, which grew after a major Taliban attack targeted his convoy in 2009.

Despite the allegations against him, Mr. Fahim no doubt played a crucial role in a multi-ethnic government that, to some degree, helped unite Tajiks and Pashtuns, the country’s two major ethnicities. After he ran for office as Karzai’s vice president in 2009, photos of his likeness were plastered all over Kabul, where they remain today.

Karzai awarded Mr. Fahim the honorary title of “Afghanistan’s Marshal” for his role during the various wars. And while many foreign diplomats raised concerns about him privately, Mr. Fahim was seen by many as a man who had accrued too much power to be dismissed or marginalized.

On Sunday, a United Nations statement called him “a good and trusted partner of the UN.”

It’s unclear precisely what role Mr. Fahim would have played in the country’s upcoming presidential elections or the subsequent political transition, but no one doubts that he would have used his political muscle to harness Tajik voters April 5 to secure his position in the next administration. Many believe he would have supported Abdullah Abdullah, also a former Northern Alliance commander. Because of his sizable following and ethnic clout, Mr. Fahim could have been a force for unity or instability, depending on how he instructed his men to behave. In that respect, he has no clear successor.

The Afghan government called for three days of national mourning, during which the national flag will be lowered to half-mast.