Kremlin critic Alexei Navalny is due back in Moscow later on Sunday for the first time since he was nearly killed last year by a nerve agent attack.
He says the authorities were behind the attempt on his life, an allegation backed up by investigative journalists but denied by the Russian government.
Mr Navalny, 44, faces arrest on his return from Germany, where he has been receiving medical treatment.
But he has appealed to supporters to meet him off the flight.
A “Let’s meet Navalny” page has been set up on Facebook (in Russian), with thousands of people saying they will go or expressing an interest, despite forecasts of extreme cold.
He has said he is almost fully recovered from the attack, that he misses Moscow and there was never any doubt that he would return.
The Russian opposition figure collapsed on an internal flight in Siberia last August and it later emerged he had been poisoned with a Novichok nerve agent.
Russian authorities have consistently denied any role in the poisoning, and the Kremlin has rejected Mr Navalny’s claims that President Vladimir Putin himself ordered it.
Why does he face arrest?
The Russian authorities have warned Mr Navalny could face imprisonment after missing a prison service deadline in December to report at an office in Moscow.
The prison service accuses him of violating conditions imposed after a conviction for embezzlement, for which he received a suspended sentence. He has always condemned the case as politically motivated.
Separately, Russia’s investigative committee has launched a new criminal case against him on fraud charges related to transfers of money to various NGOs, including his Anti-Corruption Foundation.
Mr Navalny has asserted that Mr Putin is doing all he can to stop his opponent from coming back by fabricating new cases against him.
What kind of reception will Navalny have?
Alexei Navalny has called on supporters to “come and meet me” at Vnukovo airport on Sunday, and a large crowd will likely try to do just that.
The opposition figure may be hoping for protection in numbers, concerned not only for his physical safety but the prospect of being marched off to prison on landing.
But the call for a welcome-home ceremony is also an open challenge to the man Mr Navalny accuses of ordering his murder: Vladimir Putin.
The Kremlin has repeatedly denied that, demanding proof the activist was even poisoned.
In December, Mr Putin argued that Alexei Navalny was a nobody and anyway, he actually laughed, if Russian security forces had wanted him dead, they’d have finished the job.
There were no street protests after Mr Navalny’s sudden collapse, and had he remained abroad his influence would have waned, inevitably. But he always vowed to return, despite the risk. The very public way he’s doing that suggests a man emboldened, rather than cowed, by his brush with death.