Klein is known as an important personality of life during the 18th-century Manila.Klein is known for writing a standardized Tagalog dictionary as well as the first person to describe Palau for the Europeans and to draw the historically first map of Palau, an act which practically equated to the discovery of Palau.
He is also known to write the first astronomic observation from Manila of a moon eclipse and an overview of medicinal plants in local as well as European languages as well as recipes for their usage.