Final answer:
Lena Younger, also known as Mama, best represents the theme of achieving success in a conventional way in 'A Raisin in the Sun'.
Step-by-step explanation:
In the play 'A Raisin in the Sun', the character that best represents the theme of achieving success in a conventional way is Lena Younger, also known as Mama. Lena is the matriarch of the family and has a strong belief in traditional values and hard work. She wants to use the life insurance money to buy a house for her family, which she sees as a symbol of stability and success.