Alfred Vail expanded it to include letters and some punctuation. As far as is known Joseph Henry and Leonard Gale who also worked on other parts of the telegraph had no hand in developing Morse Code. It worked. In 1948, the United States Magazine and Democratic review published an article suggesting that Morse code would reshape the English language to be "terse and condensed". Today they say similar things about Twitter. More here.
Alfred Vail wrote a history of their work that rightly credited some prior advances in telegraphy. However, in his effort to write Joseph Henry out of history, he reveals a certain bias. Back in 1832, Morse was a professor of painting and sculpture at the University of the City of New York (now known as NYU.) His knowledge of electricity came largely from lectures given by Professor James Freeman Dana of Columbia College. Joseph Henry, Professor of Mathematics, had suggested the possibility of a telegraph-like device in 1831. It's hard in that context to credit Morse with the lions share of the technology. But the code was very conceivably his own. One apocryphal story suggests Morse based his system on the quantities of movable type available at a print shop. To his credit, Vail gives sole credit for the code to Morse.
Since Vail flushed out the code (if it was him) it has changed very little. In December 2003 the International Telecommunications Union added the "commat," a @ symbol to the code. It's rendered as "· — — · — ·" Piror to that recent change, ITU officials were unsure how long it had been since a change had been introduced. The assumption is that it's the first since the start of WWII. The Modern International Morse code, or continental code, was created by Friedrich Clemens Gerke in 1848. Gerke is said to have changed at least half the letters. International Morse Code was standardized at the International Telegraphy Congress in 1865 in Paris then endorsed by the ITU. The original code became known as "American Morse code." In the 1860s to resolve technical problems on submarine the dots and dashes were keyed with opposing polarity. Any of those changes, could conceivably have been the most recent update.
The first signs of the end came with the High Speed Telegraph Committee in 1913. The Post master general convened the group to improve efficiency.Overseas duplex and triple duplex configurations were capable of sending more messages on the same cable. Telegraph code books began condensing the messages. Despite that modest improvement the 5-unit Baudot system debuted in 1909 and was better suited to multiplexed lines. (The book History of Telegraphy by Ken Beauchamp covers this in great detail.) In 1966 ASCII replaced Baudot and Morse began to look a tad archaic. It's use in telegrams had all but ceased as home telephone service was popularized.
Then the endgame: In 1995 the US Coast Guard ceased the use of Morse Code. The The French Navy followed suit in 1997 and Australia 2 years later. In 2003 the World Radiocommunication Conference dropped the Morse code requirement for ham radio licensing. In 1999 the Global Maritime Distress Safety System replaced Morse Code for distress messages. In the US, the last commercial Morse code station KPH/KFS ceremonially sent it's last Morse Code message on July 12th, 1999. They signed off with Samuel Morse's original 1844 message, "What hath God wrought."