Let me just cough up some quotes from some champions' lores:

Twitch:
"Twitch came to the League of Legends to represent himself "as the only one of his kind" (...)"

Mordekaiser:
"a being like no other emerged from the forgotten alleyways of Noxus."

Rammus:
"His search brought him across all the lands south of the Great Barrier, but everywhere he went, he was unique."

The are obviously some other "one-of-a-kind" champions: Shaco, Fiddlesticks, etc.

And now again:

"Fizz returned to find the city abandoned: his people had vanished, leaving Fizz without a clue to explain their disappearance".

Really, Riot?

Actually, it says nothing about being the last one. And he is obviously not unique. I think Fizz falls under the category of 'person whose race has vanished.'