From 1945 -1974, what president introduced important policies, changing the country with his "good" or "bad" individual influence on the times?
Every era in American history has had notable men and women who shaped their times, for better or worse.
I am assuming this is your assignment to select one of the Presidents in that time frame that you feel had the most positive or negative effect. The good news is that there is no shortage of men or policies to choose from, depending on your point of view.
There are five Presidents between 1945 and 1974, Harry Truman, Dwight Eisenhower, John F. Kennedy, Lyndon Johnson and Richard Nixon. While some might automatically argue that Nixon had the greatest (and mostly negative) influence on the times, I think I would have to go with his predecessor, Lyndon Johnson.
Besides introducing combat troops into the Vietnam War and later escalating that conflict to hundreds of thousands of troops, Johnson also created a domestic peace corps called VISTA -- Volunteers in Service to America. He convinced Congress to pass the Voting Rights Act, perhaps the most significant piece of civil rights legislation since the Civil War ended. Add to this Johnson and Congress passing the Medicare program, medical insurance for senior citizens, by a single vote. Now it is one of the most popular government programs.
His decision to enter the US into the Vietnam War divided the country and led to his deciding not to run for re-election. Nixon was then elected on the idea of withdrawal from Vietnam.