Both were gigantic egomaniacs who passionately believed themselves to have been sent by Providence to fulfill important roles in world history. The more powerful they became the more convinced they were of the almost divine importance of their respective missions. They were both, obviously, thoroughly evil individuals who had no regard for human life and no compunction in sacrificing the lives of millions to fulfill their own warped, megalomaniacal obsessions.
There were, of course, many differences between the two dictators. For one thing, Mussolini was very much a ladies' man, a notorious philanderer who cheated on his wife on numerous occasions. Hitler, on the other hand, was too fanatically devoted to his own destiny as leader of the National Socialist revolution to develop much of an emotional life.
Mussolini was less ideologically driven than Hitler. What constituted fascism in Italy was never, as a consequence, established with any degree of certainty or conviction. Policies changed with breathtaking rapidity, particularly in relation to foreign affairs. Hitler, however, was much more of a true believer in the ideology of National Socialism. His grand conception of a Nazi racial empire in Europe was markedly different in character from Italian colonialism in Abyssinia, which was largely concerned with the recovery of an imagined imperial greatness.
Despite his background as a socialist, Mussolini was less radical than Hitler. Fascism as it developed under "Il Duce" was generally a reactionary ideology used by conservative forces to counter the growing threat of anarchism and communism, especially in Italy's rural areas. National Socialism, on the other hand, envisaged a complete transformation of society along racial lines. This reflected Hitler's monomoniacal obsession with race, an obsession not shared by Mussolini.