Final answer:
The Austrian ruler responsible for abolishing serfdom and enacting reforms was Joseph II, part of the broader European trend towards liberalization and reform during the 19th century.
Step-by-step explanation:
The Austrian ruler who implemented a comprehensive reform program which abolished serfdom, eliminated internal trade barriers, and introduced a new penal code was Joseph II. These reforms were part of a larger European trend during the 19th century, driven by the changing social and economic conditions, such as the shift towards industrialization and the growing dissatisfaction of both urban and rural workers with their living conditions.
Significantly, the abolition of serfdom also occurred across other parts of Europe, influenced by rising nationalist sentiment, social unrest, and revolutionary fervor. Joseph II's reforms, while progressive, were part of a broader movement of liberalization that characterized the era, against the backdrop of nationalist and liberal movements seeking to reshape European states and societies.