Erlang was a mathematician, statistician and engineer, born in Lonborg, Denmark in 1878.  He invented the fields of queuing theory and traffic engineering.  

Erlang went to work for the Copenhagen Telephone Company in 1908 - he was the first person to study the problem of telephone networks.

It was while working for the CTC that Erlang was presented with the classic problem of determining how many circuits were needed to provide an acceptable telephone service.  He applied mathematics to assess how many operators were needed to handle a given volume of telephone calls.

He published two works on the theory of probabilities:

1909 - 'The Theory of Probabilities and Telephone Conversations'

1917 - 'Solution of some problems in the Theory of Probabilities of Significance in Automatic Telephone Exchanges'

In 1946, the International Consultative Committee on Telephones and Telegraphs, honoured him, by adopting the name 'erlang' for the basic unit of telephone traffic.