Jon Santiago is an American physician and politician serving as the Democratic Massachusetts state representative for the 9th Suffolk district since 2019. His district mostly comprises the South End neighborhood of Boston, though it also includes parts of Boston's Roxbury, Back Bay and Fenway neighborhoods. His 2018 victory in the Democratic primary unseated the chamber's assistant majority leader Byron Rushing, who had represented the district for 35 years, starting in 1983. Santiago had been a State House intern for Rushing before challenging him to his seat.Santiago continues to serve as an attending physician in emergency medicine for the Boston Medical Center, arguing that such a job informs his legislation, especially when it comes to matters of public health like the opioid epidemic.Since 2013, Santiago is a captain in the US Army Reserve. He previously served as a volunteer community health specialist to the Peace Corps.