Complex sentence: After leaving Georgetown, Dubourg founded St. Mary's College, Baltimore, serving as its President for thirteen years, during which he acquired a reputation as a spendthrift while introducing some innovations.
Split into simpler sentences: After leaving Georgetown, Dubourg became the first President of St. Mary's College, Baltimore, where he remained for thirteen years. During his time as President, he acquired a reputation as a spendthrift while introducing some innovations.