I believe it is atrributed to Henri la Fontaine a monk, who lived and worked at monastery of La Belle Plaisanterie de la Stylo in Toulouse in 1432.
Tiring of writing manuscripts with a quill, he experimented by filling chicken bladders with ink and attaching them with sellotape to the top of the sticks, the end of which was tapered to an early type of nib.
Much experimentation saw the design refined, whereby the stick had a groove carved into it, allowing for a reliable ink flow from the bladder to the nib.
This allowed the copying of manuscripts to be done much more efficiently and quickly and the output of the little monastery caught the attention of Pope Pius XI who demanded to know how it was being done.
The answer - that it was down to "la Fontaine's pen", stuck and the rest, as they say, is history.