On IRC, your "persistent identity" was your user@hostname (and your nick is ephemeral). That's why the user@hostname is shown when a client joins a channel, or

On IRC, your "persistent identity" was your user@hostname (and your nick is ephemeral). That's why the user@hostname is shown when a client joins a channel, or in WHO or WHOIS - and why bans match on nick!user@host. This worked great when people were typically using IRC from their login on a server at their university (and this is also originally why IRC servers used the 'ident' protocol when you connect - to stop you spoofing other users on the same shared system). It stopped being a viable persistent identity for all users when the @hostname part stopped being persistent - when people started gettting dynamically assigned addresses on internet connections at home.