Plato "tripartite soul" predates Freud's three-part mind. It consists of the appetitive (id), spirited (superego), and rational (ego) parts. In The Republic, he claims the perfect government reflects the human soul, being made up of three parts:
The masses, merchants and laborers, are the appetitive/id. They have a free market, always seek to satisfy their personal desires, and want as much freedom as possible.
The Military is the spirited/superego, and seeks to maintain order and the rule of law.
The government, which in Plato's ideal republic would be a group of philosopher-kings who aren't allowed to own any wealth, are the rational/ego. They command the other two groups and maintain balance between the masses' wish for freedom and the military's wish for order.
The command of the Army of Northern Virginia, at least through Chancellorsville:
Robert E. Lee: overall commander, principled but basically realistic, provided balance between Jackson and Longstreet. (Ego)
Thomas J. "Stonewall" Jackson: imaginative, risk-taking, bold, passionate. (Id)
James Longstreet: highly principled, the voice of logic and reason. (Superego)
Joseph Stalin: Like Spock, cold and calculating, noted for personal discipline (paranoid personal discipline, but discipline). (Superego).
Franklin D. Roosevelt: Like Kirk, eternally mediating between the two, knowing full well the risks of falling in either direction (fall to Winston, start World War III against Joe. Fall to Joe, lose Eurasia). (Ego)
On the other hand, the Axis Powers provide a fine example of a dysfunctional, even neurotic, relationship:
Fascist Italy: Provides the template for the Fascist form of government yet they are not as warmongering as Hitler or the Japanese, a little more rational with rejecting Hitler's genocidal methods and the Japanese ideal of Honour, but had a poor performance in the war, which forced them to ally with the Allies at the last minute (a weakened Ego)
The leaders in Paris1919 were also dysfunctional, but not as much:
Georges Clemenceau: Ambitious, feisty, and more than a little bit vindictive. This last bit gave him an intense and personal desire to see Germany pay. (Id)
Woodrow Wilson: Emphatically moral to the point of being puritanical, as well as being very cold and logical (he was not only a college professor, but he was part of the movement that tried to make political science as much like a science as possible). He insisted that the world comply with his moral conception of order, and didn't think much of anyone who disagreed. (Superego)
David Lloyd George: An easygoing, personable fellow trying to mediate between the two. He want to punish Germany but not take vengeance; was OK with the League but didn't think it was workable; he thought self-determination was nice-seeming but that concessions had to be made to power politics; and he was consistently frustrated both by Clemenceau's vengeful scheming and Wilson's sermons. Unlike most in his position, he was overshadowed; as he put it, he was sitting between Napoleon (Clemenceau) and Jesus Christ (Wilson), so no wonder the agreement was so dysfunctional. (Ego)
It didn't help that Lloyd George was simultaneously playing the Ego to the entirely British Empire delegation, most especially Billy Hughes (bombastic, vindictive Australian PM in bed with Clemenceau; Id) and Robert Borden (Canadian PM, logical, a stickler for protocol, and in an uneasy alliance with Wilson; superego). Within that, Borden himself was playing Ego to Wilson's Superego and the collective Id of the British Dominions (led by Hughes but also including New Zealand's William Massey and South Africa's Defence Minister Jan Smuts) over the issue of League of Nations Mandates (Australia and New Zealand wanted German Pacific colonies; South Africa wanted Namibia; and Canada wanted control of Britain's colonies in the Americas).
The legislature represents the will of the people. (Id)
The judiciary: Guilty or not guilty? The judiciary also has to judge if a law is constitutional (Superego)
The executive is the primary decision maker, they have to balance ideals and strategic objectives with the situation at hand, and they have to fulfill the desires of the legislature while still being under the criticizing eyes of the judiciary (Ego)
Bob Dylan: The blogger Tony of Every Bob Dylan Song made the observation (in his post about "All I Really Want To Do") that Bob Dylan's early trio of acoustic folk albums follows this pattern.
The Freewheelin' Bob Dylan: Ego (has some serious songs as well as more personal ones)
The Times They Are a-Changin: Superego (mostly serious, moralistic social commentary songs)
Another Side of Bob Dylan: Id (more lighthearted, mostly personal songs about relationships)
The three members of Rush: Neil Peart is the Superego, Geddy Lee is the Ego, and Alex Lifeson is the Id. Geddy also displays some Id tendencies but is overall more of an Ego than Alex.
On of the most popular classical 3-piece line-ups is the piano trio, consisting of piano, violin and cello. In this you have a treble instrument (violin) and a bass instrument (cello), both of which can be highly expressive in their own right, and an instrument that can be a bit of both (the piano). So violin + cello = id + superego (either way round - depends on the piece and the composer), while piano = ego.