I should point out that Leibniz had the two key ideas that you need to get this modern definition of randomness, he just never made the connection. For Leibniz produced one of the first calculating machines, which he displayed at the Royal Society in London, and he was also one of the first people to appreciate base-two binary arithmetic and the fact that everything can be represented using only 0s and 1s. So, as Martin Davis argues in his book The Universal Computer: The Road from Leibniz to Turing, Leibniz was the first computer scientist, and he was also the first information theorist. I am sure that Leibniz would have instantly understood and appreciated the modern definition of randomness.
This is the original essay I read, I think: http://evans-experientialism.freewebspace.com/chaitin.htm