Complex sentence: In his early life, Stubbs held a few odd jobs, such driving mules and being a clerk, before becoming a very successful railroad contractor; by the time he entered into politics, he was a self-made millionaire.
Split into simpler sentences: In his early life, Stubbs held a few odd jobs, such driving mules and being a clerk, before becoming a railroad contractor. His prowess as a contractor continued, and by the time he entered into politics, he was a self-made millionaire.