Cleo, one of the few girls' names to boast the cool-yet-lively o ending, is of course short for Cleopatra, the name of one of the most powerful women in history.
Cleo was most popular in the early decades of the twentieth century--when it was also used for boys. The opening of the Egyptian tombs along with the 1917 silent film starring Theda Bara popularized a range of now-obscure Cleopatra diminutives, including Cleora, and Cleola.
A distinguished bearer is the British jazz singer Cleo Laine, and there have been Cleos on two TV dramas: ER and Law & Order: Special Victims Unit.
Maybe the fact that Cleo was recently chosen by Friends' David Schwimmer will ignite a welcome revival.
Sound-alike Clio is the name of the ancient Greek mythological muse of history and heroic poetry, one that is rich with modern charm and would also make an intriguing choice,