Darius

Darius is the final boss you have to defeat in the game. He uses the Audi Le Mans Quattro (which when released was renamed the Audi R8). He is a difficult boss to beat, as his car is very fast and has excellent handing and acceleration.

Pre-boss race
Darius first appears after you fail to escape from Cross in the opening part of the game, where you wreck your BMW M3 GTR by crashing into a construction zone in Lookout Point. He appears to be calm, but also a bit rough. He gives you three cars to choose from to begin your career with, in a parking lot in San Juan.

At 25% completion, Darius drives up to you outside the safehouse under Highway 142, saying "You've almost done it. Don't give up now, you're close", then he drives off.

After you defeat the third boss, Darius will ask to meet you in the Courtyard in Downtown Palmont. He seems to be disappointed. He says "Things have progressed much further than we thought possible. It's time for you to run away again." Then he calls out Cross from the shadows, and he busts you, while Darius drives away.

Silverton
Before you start your first race in Silverton, the game plays a cutscene with Darius in it. He gets a phone call from an unknown person, who tells him the three bossess, Angie, Kenji and Wolf, have fleed their respective areas to join Darius so they can get their revenge on you.

After your first win in Silverton, Darius once again drives up to you, this time with his new crew. As always with bosses when you win your first race in their territory, he says something to you. Darius says "You think you know this town? You have no idea what's in store for you other than it's gonna hurt." He then drives off again. However, for the PS2 version of the game, Darius will say "I run everything. Cars and drivers. I've been running you all along... You're mine."

Boss race
Darius's boss races become available once you defeat Kenji, Angie and Wolf in their two sprints. It is linked on after the two races, so you can't change anything before you go to race him, it just goes straight to his race after the previous two races.

Darius's circuit race is Lucky Towers. It has a good mix of high speed sections and corners. It is good to use shortcuts, and make sure you stay ahead of him, as it is tricky to pass him back after he passes you, especially if you are using a low performance car, such as a Tier 3 Tuner or any lower Tier than 3.

The Canyon Darius uses for his Canyon Duel is Eternity Pass. The first section is moderate straights connected by tight 180 degree hairpins, while the rest is long straights connected by a series of slow-medium corners. If you have a Chevrolet Corvette Z06 or the Dodge Viper, there is a high chance that you can pass him on the first turn. If you are driving other cars, you can overtake Darius at the mini-double-hairpin halfway down the run, or the next sweeping corner, where he tends to slow down enough so you can pass him. If you can't pass him, stay close to him so you get a better gap when you do the second run.

After you defeat Darius in the circuit race and the canyon duel, you arrive back in Silverton. Before driving away, Darius gives you his car then says "The keys are in the car. [long pause] Enjoy it while it lasts. There's always someone out there who's a little faster than you are, and sooner or later they're going to catch up."

After this scene, the credits roll.

A lot of people seem to get confused by this bit, as they think his car is given to them in their garage, or to be purchased in the car lot. It in fact is not obtainable in career without the use of trainers. It is only available for use in Quick Race mode. The player actually unlocks whatever cars were not unlocked in their career (eg. defeating him in the Tuner path will unlock the 2006 Dodge Charger SRT-8, 1967 Shelby GT500, Mercedes Benz SL65 AMG and Porsche Carrera GT).