Who invented capitalization of words?

By the first century A.D., the Roman alphabet used letterforms that we recognize as uppercase, today. Between the fifth and eighth centuries, Irish monks developed a style called "Half-Uncials" which are fairly close to the letterforms we now call lowercase. In the early Middle Ages, various styles between the two were used at various places, but the majuscule Roman letters and the rounded cursive letters were not mixed.

If capitalization can be attributed to any one person, it would have to be an English abbot named Alcuin of York, who worked in the monastery at Tours during the reign of Charlemagne. Following a Church decree issued in 789 A.D., Alcuin developed a style of calligraphy that mixed the majuscule and minuscule letterforms. He systematized punctuation, visibly dividing text into sentences and paragraphs, and placed capital letters at the beginning of each sentence.

See link below for examples.