Since the Battle of the Trident is such a formative event in the backgrounds of many characters, we have developed certain minor details around the framework of events established in the books. For the reference of those characters whose lives would be effected by that battle, here's the deal…
Fought in 283 A.L. across a series of fords at the Green Fork of the Trident river, the battle was a three pronged assault by the rebel forces to break the Royal host which blocked their advance on King's Landing. While the royal host was larger at about 40,000 men, the Rebel host (of about 35,000) had seen more battle, and- tellingly- more victories. Those named below are by no means an exhaustive list, simply an outline of notable people characters might be aware of.
Deployment of forces:
Rebel Host (35,000 men)
Rebel Right: apx 11,000
Northmen under the command of Eddard Stark
-Houses present: Stark, Karstark, Umber, Mormont, Glover, Tallheart, Flint, Bolton, Hornwood
-Knights present: Rodrik Cassel, Marc Ryswell
-Non-knightly nobles present: Benjen Stark, Willam Dustin, Anders Flint, Connell Flint (died in this battle)
-Non-knights present: Kell Drakmoor, Marsden Streem, Pariston Vis
Rebel Center: apx 15,000
Loyal lords of the Stormlands and Riverlands under the command of Robert Baratheon
-Houses present: Baratheon, Grandison, Caffern, Fell, Mallister, Terrick, Bracken, Piper, Vance
-Knights present: Lord Jason Mallister, Jerold Terrick, Geoffrey Tordane, Cyric Valentin, Anton Valentin, Hardwicke Blayne, Martyn Mallister, Kamron Mallister, Wayland Frey
-Squires present: Jacsen Terrick, Jarod Rivers, Gedeon Rivers, Hollister Slane, Keelin Dorsey, Darion Terrick
-Non-knightly nobles present: Rafferdy Nayland
-Non-knights present: Solomon Wake
Rebel Left: apx 9,000
Loyal Lords of the Vale and Riverlands under the command of Jon Arryn
-Houses present: Arryn, Royce, Corbray, Waynewood, Belmore, Egen, Hardyng, Blackwood
-Knights present: Lyn Corbray, Yohn Royce, Bruce Longbough
Royal Host (40,000 men)
Royal Left: apx 12,000
Riverland and Vale Loyalists, and some Crownlands troops under Jonothor Darry of the Kingsguard
-Houses present: Darry, Goodbrooke, Whent, Mooton, Stokeworth, Hayford, Chelstead, Groves
-Knights present: Rygar Nayland, Stafford Groves, Kittridge Groves, Nicodemus Groves, Rutger Nayland,
Symeon of Sevenstreams
-Non-knights present: Tommas Belte, Dominick Augusten, Raylan Weir
Royal Center: apx 18,000
Crownlands houses under the command of Prince Rhaegar Targaryen
-Houses present: Targaryen, Cressey, Farring, Gaunt, Manning, Staunton, Thorne, Selmy
-Knights present: Barristan Selmy
Royal Right: apx 10,000
Dornish under the command of Lewyn Martell of the Kingsguard
-Houses present: Martell, Dayne, Santagar, Dalt, Fowler, Jordayne, Wyl, Yronwood, Manwoody, Uller
Both armies drew up within sight of each other, the rebels approaching from the north with the royal line drawn up defending the main crossing of the Green Fork. Both generals approached with a similar battle plan of advancing their right wing in support of a charge in the center, seeking to roll up the enemy's flank, while holding ground with their left wing. The clash of the Vanguards was very bloody, with neither side willing to fall back, even as the Center divisions were ordered in to their support.
On the royal right (rebel left) a strong advance by the Dornishmen under Lewyn Martell was threatening to drive back the rebels under Jon Arryn, with the Vale lords losing ground under concentrated pressure. Although Lewyn Martell has been wounded, the Dornish advance was not stopped until a counterattack of Riverlords anchored by the Blackwoods broke the Royal lines, allowing Lyn Corbray to kill the wounded Kingsguard Ser Lewyn Martell. This led to a collapse of the royal Right, as the Dornish lords retreated back across the Green Fork and fled the field.
On the rebel right wing (royal left), the Northmen charged hard against many of the same men they had defeated shortly before at the Battle of the Bells. Wise enough not to waste his cavalry against the tightly packed royal lines, Stark relied on the weight of his infantry in the assault. Fighting here was stubborn, and- despite heavy casualties, the royal lines held against the Northern onslaught, although Ser Jonothor Darry was badly wounded in driving off the first charge. While the royal morale wavered as Ser Jonothor was taken behind the lines, discipline was maintained and re-ordered in time to meet the second charge of the Northmen. At about the time Lyn Corbray's counterattack broke the royal right, the men of the left threw back the second assault of Eddard Stark's footmen, again at great cost to the defenders.
Meanwhile in the center of the field, Robert Baratheon's frontal assault had managed to slowly push back the defending line of royalists, culminating in the charge of Jason Mallister's knights which managed to pierce the center of the set-upon royal lines. In the ensuing press, Barristan Selmy was badly wounded, and rumored to have been killed. Troops of the royal center began falling back across the Green Fork, heavily pressed by Robert himself and the other knights of the rebel center. As the royal right wing collapsed, Prince Rhaegar rallied the center and counterattacked to check Baratheon's advance. This is the point at which Geoffrey and Geonis Tordane were killed.
At this point, with the rebel left advancing to flank the royal center, the most famous duel of the war took place as Robert and Rhaegar fought in the shallow waters of what would become known as the Ruby Ford. With Rhaegar's death, the royal center collapsed and fled the field, or surrendered. Among the captured wounded was Barristan Selmy. The last organized resistance to the rebel army (the royal left) withdrew in good order from the field, lowering their banners soon afterward, when the full scope of the disaster became apparent.
At this point, with Robert and much of the rebel cavalry wounded, the Frey host arrived on the field pledging to Robert's support. Command of a reformed rebel Van was organized under Eddard Stark who rode ahead of Robert's battered army to King's Landing with a strong body of knights, some of whom were Charlton men of Frey allegiance, while the majority were of Stark's own intact cavalry.
Of the wounded Kingsguard, Ser Jonothor Darry died of his wounds, while Barristan Selmy survived. A general pardon was issued by Robert for all those who defended the Targaryens against him, but many of the more prominent Royalist families suffered the loss of some lands and properties, which were awarded to those who had sided with Baratheon. Following the death of King Aerys, many knights were dubbed (Jarod Rivers later commented that "Most squires with four limbs still attached were dubbed"), and several worthy smallfolk were elevated to nobility, such as Cyric Valentin.
Besides Robert himself, the most popular heroes of the day were Lyn Corbray who slew Lewyn Martell, and Jason Mallister who carved open Robert's path to Prince Rhaegar. After the battle, Robert famously send his own maester to tend the injuries of the badly wounded Barristan Selmy.