Don Paolo

"Layton has been my archnemesis ever since that fateful day!"

- Don Paolo about his grudge against the Professor

Don Paolo is considered one of the primary antagonists of the first trilogy of the Professor Layton series of videogames (while Jean Descole is the primary antagonist of the second trilogy) and considers himself Layton's archrival, a claim supported by the fact he is considered a criminal mastermind within his own setting and was a scientist of the highest nature - however he was expelled from his position due to his unethical nature. He is also a master of disguise.

Professor Layton and the Curious Village
Wanting to find the treasure of the Reinhold family Layton was searching for, Don Paolo would become the main villain of Professor Layton and the Curious Village where his profile gives a rather unique insight into his personality as it notes that when not committing evil deeds Paolo is fond of listening to music. Furthermore he disguised himself as Inspector Chelmey to frame Layton in a murder case.

Professor Layton and the Diabolical Box
In Professor Layton and the Diabolical Box Don Paolo shows his skill of disguise by successfully managing to play the part of Don Flora - being able to fool many into believing he was her, according to the profile he was so good at this he was even able to mimic her walk. Disguised as Flora, he wanted to solve the mystery of Anthony Herzens Elysian Box he had stolen from Laytons's mentor Dr. Andrew Schrader.

Professor Layton and the Unwound Future
It is also revealed that Don Paolo's rivalry with Layton stems from the fact his love, Claire, was in a relationship with Layton - this embittered Paolo towards Layton and he swore revenge: an oath he seems to live by until he teams up with Layton in Professor Layton and the Unwound Future to solve the mystery of future London and stop Dimitri Allen. He also helps saving London from Clive.

Trivia

 * He was also briefly seen in the beginning of the movie "Professor Layton and the Eternal Diva", where one of his plans was foiled by Professor Layton.
 * In the Professor Layton manga he is depicted as a comedic and incompetent On & Off villain, rather than an actual threat.