Short answers, pulled from the story.
The Gauls emerged around the 5th century BC as bearers of La Tène culture north and west of the Alps. This cultural development followed the Iron working Hallstatt culture from the 8th century BC.
By the 4th century BC, these tribes controlled trade routes along major river systems including the Rhône, Seine, Rhine, and Danube. Their homeland known as Gaul stretched across what is now France, Belgium, Switzerland, Southern Germany, Austria, and the Czech Republic.
A reassembled Greek army defeated the Gauls after they passed through Thermopylae and headed for the treasury at Delphi. The leader Brennos was seriously injured at Delphi and committed suicide there before survivors fled back toward Macedonia and eventually Asia Minor.
Julius Caesar launched the Gallic Wars in 58 BC and had conquered all of Gaul by 51 BC. He noted that the Gauls called themselves Celtae while Romans called them Galli.
A genetic study published PLOS One December 2018 examined 45 individuals buried La Téne necropolis Urville-Nacqueville France identified as Gauls. Another study Journal Archaeological Science October 2019 examined 43 maternal 17 paternal lineages La Téne necropolis Urville-Nacqueville plus 27 maternal 19 paternal lineages La Téne tumulus Gurgy Les Noisats near Paris.