Blog is generally thought to be a contraction of the word 'weblog', which itself could be extracted to be 'World Wide Web Log Book'. What people generally don't know that this belief is a mistaken one.
The word blog actually comes from the Latin blogadarium ululare (literally 'the howl of seemingly informed') however its precise date of inception is still figures in debate amongst scholars.
The First Blogger
The first blogger was born Otho de Lagery, and later went on to become Pope Urban II between 1088 and 1099. His papacy spanned the First Crusade and it was the reports and hearsay from Jerusalem that inspired him to write.
Urban II felt dissatisfied that the message in his personal writings, his diary and his pronouncements were being insufficiently heard, and thus made the decision to write about his daily activities on the outer walls of the Apostolic Palace. In the early days of this process, Pope Urban II was dedicated - writing missive missives most days, sometimes more than once in day. Later on, the textual content became less, and he focused more on pasting up icons of his favourite saints, and sometimes tapestries illustrating stories from the empire that he found amusing. When questioned in 1091 about whether the scrawl on the Palace has a particular, he responded "Ridevo ut ridero" - "I used to laugh, and I wish to laugh again".
Pope Urban II dealing with 'A trollage of Cardinals' in response to a controversial post some found to be factually incorrect
It was not however until the papacy of Callixtus II where this activity became untenable. Callixtus II believed that a response from the souls of the 'virtuous subscribers' could be a complex message from the divine, and thus left a space underneath his pronouncements for the 'release of holy response' - which in modern times we like to think of as 'comments'. Unfortunately, the Apostolic Palace was falling into disrepair by this point, and also there was very little room left on the walls.
The period of inactivity lead to the rebuilding of the Vatican under Pope Sixtus V, who regarded the wall writing as beneath the dignity of holy office, and believe there were higher and holier arts. Thus the blog inadvertently lead to what we now consider one of humanity's greatest works - the Sistine Chapel. To this day, if you look closely at how Michaelangelo has spaced certain features, you can just about make out the word lulsate, where we get our modern lulz from today.