102444
Designed by Robert Stephenson , the class was introduced into service between November 1838 and November 1841 , and withdrawn between April 1864 and September 1871 .
 Robert Stephenson
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 Robert Stephenson