Despite the ideological differences, Iran and Syria have for decades aligned on key Middle East issues - such as during Lebanon's Civil War - forming a powerful axis aimed at countering US, Saudi and Israeli influence in the region.
The Arab Spring saw Tehran and Damascus work together again, to suppress a pro-democracy uprising in Syria with Iran seeing Bashar Al-Assad's survival as critical to its overseas interests and the survival of its own regime in the long term.
Before his death in January, Iranian Revolutionary Guards Corps' (IRGC) general Qasem Soleimani had built up a force of thousands of foreign fighters, flown into Syria under the pretext of defending the Sayyida Zainab Shia Muslim shrine outside Damascus.
Later, Soleimani was effectively overseeing the Assad regime's ground campaigns through a nexus of local and foreign militia forces.
The cost for Iran in propping up Assad is estimated to be around $15 billion a year, although analysts stress that the real figure could be even higher.
The human price has been thousands of dead Iranian and foreign fighters and major damage to Tehran's reputation in the Sunni-majority Arab world, with few or no discernible benefits for the Iranian people.
"The major goal of Iran was to save the Syrian regime from collapse, and they have achieved that. But have they gained enough influence to make Iranian sacrifices in Syria worthwhile? The proclaimed economic benefits are less likely to materialise," Mohanad Hage Ali, director of communications and a fellow at the Carnegie Middle East Center told The New Arab.
"The impression, internally, is that Iranian money is being spent on external causes which only bring Iranians sanctions rather than potential benefits. This is why there is an effort by the Iranian regime to portray Iran as benefiting from these external interventions. It's not just free help, there's some economic benefit there."
Russia appears to have accrued more rewards from its intervention in Syria than Tehran - and with a fraction of the manpower losses due to its focus on aerial bombing rather than ground operations.
Iran's mobilisation of the National Defence Forces militias in Syria has been only partly successful due to the group's poor reputation as a fighting force and tendency towards bribery and brutality.
The establishment of IRGC-led foreign militia corps - manned mostly by Afghan, Iraqi, Lebanese and Pakistani Shia Muslim fighters - has helped the Syrian regime win back major cities.
Iran has also partially established a land corridor from the Mediterranean to Iran, but in general the rewards accrued by Tehran do not reflect its sacrifices in the war.
Today, IRGC bases are open game for Israeli and US jets in Syria. Its huge militia army in Syria mirrors Tehran's own political model but this parallel state has led to distrust in Damascus. which favours a centralised authority mirroring Vladimir Putin's form of governance.
The Russian and Syrian regimes share the same authoritarian and relatively secular nature, as opposed to the explicit sectarian identity of Iran's Shia militias, Hage Ali said.
"Syria's claimed secularism is also a form of Alawi sectarian identity, in the face of Sunni religiosity. To a certain extent, the Iranian militias' sectarian identity is irritating to the regime," Hage Ali said.
"Perhaps this is another reason why the Russian intervention proved to be more enduring and durable in terms of expanding [Moscow's] sphere of influence within the regime and the army."
Russia is also keen to see Damascus returning to the Arab fold and sees Syria's political normalisation with the US and Europe as another goal, in order to boost the country's economy and bring in reconstruction money.
The perception in the regime that Moscow is a more reliable and relatable ally than Tehran has seen Russia win a long list of political, military and economic rewards.
Although Syrian regime media is full of news about trade deals and memorandums of understanding signed between Iran and Syria, business analysts have questioned how many of these could ever come to fruition.
Former US president Barack Obama's focus on the threat from the Islamic State group and Al-Qaeda, saw Iran increase its clout in Beirut, Sanaa, Damascus and Beirut.
This came at little political cost for Tehran and when a nuclear deal was agreed in 2015, US sanctions on Iran were eased.
In Donald Trump's term in office, however, the US has sought to contain Tehran by enforcing crippling sanctions on Iran's oil and banking sectors.
Tehran is still lumbered with high costs in maintaining the IRGC's presence and proxies abroad, with increased scrutiny about this burden during difficult economic times for Iran.
Yassamine Mather, Senior Researcher at the University of Oxford, told The New Arab that IRGC funding has become an increasingly divisive subject in Iran, where ordinary Iranians are beginning to suffer US sanctions.
"The way IRGC divides this income in terms of internal and external expenditure is not transparent. There is opposition to IRGC expenditure in Lebanon amongst ordinary people, but the supporters of the regime support such expenses," Mather said.
The Quds Force' campaigns against IS in Iraq were perceived by many Iranians as essential to the country's defence. Following IS' defeat, there is growing scrutiny about the IRGC's role and purpose abroad.
The recent suppression of peaceful demonstrations in Iraq by Tehran-sponsored militias has highlighted the IRGC's penchant for thuggish violence and an obsession with control.
"The government had convinced sections of the population that in order to stop IS attacking Iran it was necessary to fight in Syria and Iraq, there was less resentment about that. But this has changed since IS is no longer perceived as a major threat," Mather said.
The IRGC's murky business empire is well-known in Iran and has helped the military wing stay afloat during US embargoes.
"The IRGC budget doesn't work as percentage of the state budget… it owns or part-owns a sizeable part of 'privatised' industries and shares in banks, financial institutions in Iran and abroad," Mather added.
"It controls imports and can import goods with a much better exchange rate than anyone else. Then the goods are sold at the current exchange rate. They are also involved in the distribution of some essential services."
According to the IMF, Iran's economy could contract by 10 percent due to sanctions effectively cutting off Tehran's economy from the rest of the world.
Subsidies on fuel have been lifted in a bid to improve government finances, but hit working and middle-class Iranians hardest.
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This has led to mass outbreaks of unrest late last year, resulting in a violent crackdown by IRGC-affiliated militias with around 1,500 protesters dead.
The IRGC and conservative elements in Iran have profited from the "siege economy" through their control of the black market and smuggling rings.
"In general, there is more opposition to corruption and cronyism, where black markets have allowed allies of the regime to become super rich. The gap between rich and poor is growing, and some people indirectly or directly associated with the IRGC are among this super rich (class)," Mather added.
The IRGC is dealing with new external dynamics that could still drag Tehran into more costly regional conflicts.
The killing of Soleimani in January's airstrikes indicates that Trump will take a more robust approach to containing Iran than his predecessor.
Iran's proxy rule in Iraq (oil-rich, but lacking basic public services), Yemen (ever on the brink on famine), and Syria (a failed, violent and bankrupt state) has made Iran an undesirable political partner.
The killing of 1,500 young protesters in Iran by security forces and hundreds of activists in Iraq by pro-Tehran militias show that Iran's response to demands for basic services and jobs is brute suppression.
Arash Azizi, a writer, translator and PhD student at NYU said that while many Iranians once saw the IRGC through a nationalist prism, the force is now perceived as Ayatollah Ali Khamenei personal "Praetorian Guard".
"He has succeeded in that the Guards are - for the most part - Khamenei loyalists and ultra-conservatives or hardliners," Azizi said.
"They attempt to defend the Islamic Republic, carry it on to the new generation and counter the reform efforts initiated by the likes of Khatami, or the pragmatist orientations offered by the likes of Rafsanjani or his acolyte, Rouhani."
On a regional level, Tehran's argument on "stability at all costs" and paranoia of "foreign meddling" now appear stale and hypocritical given the mass slaughter Iran unleashed in Syria to keep Assad in control.
"I think there is a general non-interventionist mood about the Iranian population," Azizi said.
Protesters in Iraq have railed against Tehran's influence in the country, while pro-Hezbollah elements in Lebanon (as well as non-Iran aligned factions) have become targets of activists in a second wave of Arab Spring unrest, seeking to end authoritarianism, cronyism and sectarianism.
Perhaps the biggest price for Iran is that its image as a vanguard of the Palestinian cause has suffered irreversible damage over the past nine-years, given the acts of mass slaughter its forces have committed in Syria, Hage Ali believes.
"The significance of the Syria war is often understated not just in the perception of Iran but also the Arab-Israeli conflict - the Syrian regime has dwarfed Israeli crimes in the Palestinian territories," said Hage Ali.
"The Palestinian attempt to stir Arab emotions and mobilise support has been seriously impaired by the Syrian conflict. From that perspective, the Syria conflict has changed Arab perceptions of Iran significantly and caused a paradigm shift in Arab opinion."
Paul McLoughlin is a news editor at The New Arab.
Follow him on Twitter: @PaullMcLoughlin