Yan is a surname in several languages and the pinyin romanization for several Chinese surnames, including "严 (嚴)", "晏 (晏)", "偃 (偃)", "颜 (顏)", "言 (言)", "燕 (燕)", "阎 (閻)", "闫 (閆)", "鄢 (鄢)" in simplified (traditional) form.
As such, individuals and institutions who had to romanize their Chinese names prior to that time, such as when having their books translated or publishing manuscripts outside of China, used "Yen" instead of "Yan".
The Yan surname in Taiwan is mostly spelled as Yen since only until recently has the government approved the use of pinyin romanization of names.
As such, most people from Hong Kong and Chinese diaspora that emigrated prior to 1949 from Guangdong use the name Yim.
His ancestor was called Yan An who inherited a piece of land, which later flourished into the Zhu kingdom, a feudal state of Lu.