His early formal education was poor, but he proved himself to be keen observer of the world and people around him, a fact that was clearly demonstrated in all his writings later on.
He worked at a variety of jobs: printer, Mississippi river-pilot, soldier (in the Civil War), gold prospector, timber speculator and journalist. In this last capacity he worked with Artemus Ward and Bret Harte and was led, inevitably, into writing.
In 1865 he published The Celebrated Jumping Frog of Calaveras County which made him famous very quickly. He then became a full-time author and lecturer.
His pseudonym of 'Mark Twain' was one of the calls of the leadsmen who played such an important part in navigating the paddle-boats through the treacherous shifting sand-banks of the Mississippi river. The cry of "By the mark twain" meant there was a depth of 2 fathoms (6 feet) in the water at that point. Not a lot!

He married Olivia Langdon in 1870.

The later part of his life was heavily over-shadowed by several misfortunes. He was bankrupted by some ill-advised investments in 1884 and the rewards from much of his later work were needed to pay off his debts. One of his daughters died in 1896, his wife in 1904, and another daughter in 1909.

He became a well-known celebrity in an age when such 'titles' had to be earned by a lot of hard work and a display of some considerable talent.

He died in Redding, Connecticut, on 21st April 1910 aged 75.

Some of his works are:
1869   Innocents Abroad
1876   Adventures of Tom Sawyer
1882   The Prince and the Pauper
1884   Adventures of Huckleberry Finn
1889   A Yankee at the Court of King Arthur