The death of John F. Kennedy prompted the government to place his portrait on the half dollar, ending the brief rule of Benjamin Franklin, who was featured on the half from 1948 through 1963. The JFK half has ruled over a number of declines. The first year of issue (1964) was the last of the 90% silver coins. Unlike the quarter and dime, however, the half dollar contained 40% silver from 1965 to 1970. By 1971, all of our major coins were clad.
The JFK legacy
John
F. Kennedy was best known as an orator. He manhandled Richard Nixon in a televised debate in 1960. Nixon learned his lesson from the debates. For future debates, he would wear makeup. Kennedy is known for many quotations including "Ask not what your country can do for you; ask what you can do for your country." From his inaugural address. Kennedy committed the US to landing on the moon “not because (it is) easy, but because (it is) hard.”
President Kennedy was assassinated on November 22, 1963. Within three months, the Kennedy half dollar was introduced. Most of the original 1964 half dollars were hoarded, initially as souvenirs of Kennedy, and then because of their silver bullion value.
Return of the glory of the american eagle 
As required by law, all coins of denomination twenty five cents and higher must have the American Eagle on the reverse. The Franklin half technically had an eagle -- but it looked more like a bat and was only a fraction of the size of the liberty bell. On the Kennedy half, the eagle returned in its full glory as depicted on the presidential coat of arms.
Bicentennial Half Dollars
The bicentennial era In 1975 and 1976, the quarter, half dollar, and dollar were dual-dated 1776/1976. The reverse of the bicentennial half dollar depicted Philadelphia’s Independence Hall.
The 1998S matte finish Kennedy Half dollar
The most valuable Kennedy half dollar was a special matte finish half dollar produced in San Francisco in 1998 as part of a set that included the Robert F. Kennedy Commemorative dollar coin. The Kennedy half alone often sells for more than the set.
Artificial half dollars?
The last Kennedy half dollars were released for circulation in 2001. Since 2002, the mint has continued to make the Kennedy halves in proof and uncirculated form for collectors. The mint produces regular and silver proof coins. Since the Kennedy halves are not spent, they have evolved into artificial coins, whose main value is the money they produce for the mint.