On Steam (Vapeur in the Lab), a player can change username at will, but not their account ID. That ID has three forms: STEAM_0:Y:Z in game server logs, [U:1:W] in recent versions, and a 17-digit number in the profile address. Paste one of these forms (or a profile address): the tool gives the others.

In real life: steamid.io, steamid.xyz, SteamDB. A profile's username history (« anciens pseudos ») and the fixed ID make it possible to follow a player who changes names, then pivot to their other networks.