Watch your thoughts; they become words.
Watch your words; they become actions.
Watch your actions; they become habits.
Watch your habits; they become character.
Watch your character; it becomes your destiny.
Commonly attributed to Frank Law

Character is what you are in the dark.
Dwight L. Moody (1837-1899), American Evangelist

What lies behind us and what lies before us are small matters compared to what lies within us.
Ralph Waldo Emerson, American essayist, philosopher and poet (1803-1882)

The best index to a person’s character is (a) how he treats people who can’t do him any good, and (b) how he treats people who can’t fight back. 
Abigail van Buren (Pauline Esther Friedman), (1918-2002)

The proper time to influence the character of a child is about a hundred years before he’s born.
William R. Inge, American playwright (1913-1973)

Every man has three characters: that which he shows, that which he has, and that which he thinks he has.
Alphonse Karr, French journalist (1808-1890)

Character cannot be developed in ease and quiet. Only through experience of trial and suffering can the soul be strengthened, vision cleared, ambition inspired, and success achieved.
Helen Keller, (1880-1968) American blind and deaf writer/lecturer

Good character is more to be praised than outstanding talent. Most talents are, to some extent, a gift. Good character, by contrast, is not given to us. We have to build it piece by piece — by thought, choice, courage and determination.
John Luther