Who is Servius Tullias from The Early History of Rome: Books I-V and what is their importance?

Servius Tullias is one of the Kings of Rome. He is referred to in Book 4. Tullias was from Corninculum. He is described in a speech as an example of the way men have the ability to rise in the ranks amongst the people of Rome. It is being argued that this is the real justification for their success rather than their socioeconomic status.