User: Who are the best starting MLB pitchers of all time?
Assistant: There are many ways to argue who the best pitchers of all time are.  Some of the criteria to consider are Cy Young Awards, ERA titles, strike out titles and records, post season success, and longevity.  With these criteria heavily considered some of the best MLB pitchers of all time could be as follows.

5. Roger Clemens (The Rocket) pitched for 24 seasons and compiled accolades such as a record holding 7 Cy Young Awards, an MVP title, 5 strike out titles, 7 ERA titles, and won 2 World Series titles. 

4. Pedro Martinez had the 4th highest win percentage in history, won the world series, won 3 Cy Young Awards, an MVP Award, and is one of only 4 pitchers to ever have more than 3,000 strike outs while walking fewer than 1,000.  

3. Randy Johnson (The Big Unit) played for 22 MLB seasons and is the all time record holder for Wins, ranks 2nd all time for strike outs, won 5 Cy Young Awards, won The World Series. 

2. Cy Young is one of the most legendary pitchers of all time and the annual award for the best pitcher in each MLB league is named after him. Some of his many accomplishments are that he is the all time leader for wins, innings pitched, and complete games. 

1. Walter Johnson (The Big Train) was one of the "First Five" inaugurated into the MLB hall of fame.  He is the all time leader in shut outs and was the all time leader for strikeouts for more than 55 years.  He won The World Series and also is the all time leader for leading the league in strike outs 12 times.