A soldier is being remembered on the 90th anniversary of the act of bravery which earned him the Victoria Cross.
Sgt Rees also fought in another key battle at Mametz Wood in 1916
More than 60 members of Ivor Rees' family will gather in his home town Llanelli to see a plaque unveiled.
Sgt Rees, 26, risked his life to lead the capture of a machine gun at Ypres in Belgium in World War I, an act which it is said saved many Allied lives.
His son and daughter are among those paying tribute. Sgt Rees later became a council official and died in 1967.
The VC was awarded for the "most conspicuous bravery in attack" on 31 July, 1917, while serving with South Wales Borderers during the third battle of Ypres, known as Passchendaele.
His platoon dealt with a machine gun at close range, which had been causing "many casualties".
Sgt Rees edged forward gradually to try to reach it, leading around 20 of his men.
Sgt Rees' Victoria Cross is held at the regimental museum at Brecon
The citation reads: "When he was about 20 yards from the machine gun he rushed forward towards the team, shot one and bayoneted another.
"He then bombed the large concrete emplacement killing five and capturing 30 prisoners... in addition to an undamaged gun."
Lt Col David Mathias, of the Royal Naval Association in Llanelli, which is helping to organise the tribute at the town hall, said it was hard to estimate how many Allied lives he saved by his actions.
"I grew up a couple of streets away from him and we had Rees the baker, Rees the postman and Rees the VC," he said.
"My grandfather took me to meet him once when I was a boy and he was a genial gentleman."
Passchendaele was fought in the wet season in 1917
Ivor Rees had joined up as a steelworker in 1914 but was quickly promoted to sergeant.
After the war, he was unemployed for a couple of years back home in Llanelli before starting work with the council, where he rose through the ranks to a head of department.
During World War II, he served with the home guard.
"What we're remembering isn't what he was before the war or after the war but what he did during the war - he was a ferociously good soldier," said Lt Col Mathias.
Major Martin Everett, curator of the Royal Welsh's regimental museum in Brecon, where the medal is now held, said he had met Sgt Rees before his death in 1967.
He remained a modest man, carrying with him the memories of comrades lost.
"When you read the story of Passchendaele, the battle bogged down in all that mud, you can't quite believe what those lads went through," said Maj Everett.