Spain has four special names for unknown or forgotten people: these are Fulano, Mengano, Zutano and Perengano. The most used is Fulano, 'Whassisname', which comes, apparently, from the Arabic: fulān which means 'anyone'.
Mengano, or 'Whojammie', is also from the Arabic man kān and means 'whoever'. The other two names, 'Thingy' and 'Spike' are used less. The first, Zutano, may come from scitānus, Latin for 'wise one', but it's anybody's guess about Perengano.
The Spanish use these names for handy reference, Fulano and Mengano above all.
The diminutive version, Fulanito, is particularly useful for jokes, along the lines of 'little Jimmy'.
The female of Fulano, Fulana, is used (as is always the way) pretty much exclusively to mean a puta.
And now, looking at Wikipedia, I find all sorts of other versions, in every language: including Miðalhampamaður from the Faeroe Islands.
I know, time to go and do some work...