Senator Edward ‘Ted’ Kennedy (D-MA) has died at the age of 77. Kennedy, who has served in the U.S. Senate since 1962 and was the second-most senior member of the body, was diagnosed last year with terminal brain cancer.

The youngest brother of President John F. Kennedy (D) and Senator Robert F. Kennedy (D-NY), both of whom were assassinated in the 1960s, Ted Kennedy has been a polarizing political figure receiving both praise and derision from political opponents and observers. He has been alternately lambasted as one of the Senate’s most liberal members and praised for reaching across the aisle and his extraordinary effectiveness as a legislator. For example, Kennedy set the tone of the highly politicized 1987 confirmation hearings of Robert Bork, who had been nominated by President Ronald Reagan (R) to the U.S. Supreme Court, and political ideology—which was traditionally off-limits during confirmation hearings—became a standard topic of debate. However, Kennedy was also instrumental in passing the bipartisan ‘No Child Left Behind’ act, which he developed working closely with President George W. Bush (R) in 2001.

Kennedy has also been both praised and criticized as one of the most prominent Catholic politicians in the United States. He has been a vocal proponent of many ‘Catholic’ causes, including availability of health care, education, civil rights, and disabled rights, but has also been criticized for his support of abortion rights in sharp opposition to one of the most fundamental Catholic moral teachings.

Under current Massachusetts law, Kennedy’s replacement will be selected by special election. Shortly before his death, Senator Kennedy wrote a letter to the Massachusetts legislature recommending the law be changed to permit the governor to make a temporary appointment. It is unclear at this time if the law will be changed per Kennedy’s request. Known as the ‘Lion of the Senate’, Kennedy is well respected by many members of both political parties. He is survived by his wife Victoria, ex-wife Joan, and five children.