King Zhaoxiang of Qin
Reigning over 55 years, he was one of the longest-serving rulers during the Eastern Zhou Dynasty. Although making numerous policy mistakes during his later years, his aggressive territorial expansions were pivotal in consolidating the state of Qin as the dominant military powerhouse in the late Warring States period. It was the strategic dominance established during his reign that paved the way to Qin's eventual successful unification of China under his great-grandson, Ying Zheng.
Marquis of Qin
Although Qin would eventually develop into a major power that would conquer all other Chinese states and unite China in 221 BC to start the Qin Dynasty, at the time of the Marquis of Qin it was still a minor state of the Western Zhou Dynasty classified as an "attached state" (附庸, "fuyong"). Qin rulers did not receive any nobility rank until four generations later during the reign of Duke Xiang of Qin, so "the Marquis of Qin" was presumably an honorific posthumous title that his descendants used to refer to him.