Chuck Knoxville, better known as Nitro, is a racing legend, and founder of the CSR program. With the introduction of the World Tour and International portions to single player, he becomes the main deuteragonist of the storyline.
Knoxville founded the CSR, and participated within races himself, establishing a legendary record in the process. However, he apparently died in a race against Papa Biz. All of the crew leaders bar Alieda will mention Nitro in their calls between crew leaders, and Papa Biz is apparently obsessed with the legend of Nitro, so much that Yoshiro has to tell Papa Biz that his obsession with him does him no favors.
After the player defeats Errol and becomes the new top dog of the CSR league, Knoxville will call the player's agent, who puts the player on the phone with him. Knoxville reveals himself to the player as the legend Papa Biz and others mentioned, and informs the player that he was the one that gave the $25000 donation to the player for their first car. He tells the player that he did fake his death during a race with Papa Biz as to retreat from CSR, having tired of participating in the league. He also jokingly warns the player not to tell Papa Biz that he is alive. Knoxville also gave an extra million dollars for buying an International crew's car.
In the World Tour portion, Knoxville will tell the player that he's "gathered some friends" to race against from across the globe, and gives the player some instructions as to how World Tour works.
In the International, during the four cups, CSRN and Roman will eventually secure an interview with Nitro, claiming that he is, in fact, alive, and is the opponent of whomever gets through all four cups without elimination. He will publicly announce Papa Biz's real name (it's Jamal) in an interview with Roman, and gets cut off when Roman ends the interview right then and there.
Roman will interview Nitro a few more times during the four cups, with Nitro explaining how some portions of the tournament will work, and that he actually organized the World Tour in secret.
During La Finale, the crew leaders will race against the player as to research how the Ferrari FXX K can be improved upon, as Nitro will race in a fully upgraded FXX K for the Finals. All of the crew leaders will question Knoxville's new, lavish antics to promote CSR in conversations with the player, and some will express their distaste of the changes, with Carlito even mentioning that he left CSR and jokingly mentions he should get Nitro to publicize his pub.
During the Finals, Knoxville will have a conversation with the player after each race, explaining his business strategies. The main reason for his unpopular strategies is because CSRN bought out the CSR league, and because of this, actually uncovered Nitro's involvement with the World Tour. He also informs the player that he is responsible for putting several racers on the map, including La Stella, Cypher, and Pierre-Yassine, with donations. With the bad situation and the truth being revealed, Chuck wishes to put things back to normal. He also expresses his disdain for Roman, telling the player to "ignore him", and that he'll take care of Roman.
Roman will interview Nitro after he and the world tour crew leaders lose the relay race to the player. Roman, expecting Nitro to shift the blame to one of the world tour racers, is taken a bit off guard when Nitro explains to him that it was the fault of no-one, and that was part of CSR's beauty: Nitro and his team simply lost, nothing more.
Eventually, Knoxville exclaims to the player that he wants to officially retire from CSR Racing, stating that the fate of the sport lies with rising stars like the player, not past legends like himself. He states that he wanted the player by his side, as he/she was the only person Knoxville could rely upon to improve the fate of the sport.
When the player defeats Nitro and the International rivals in a five-man relay race, Nitro will have an interview with Roman, who was put in a call with Nitro on accident, being misinformed and believing that Nitro won the race. At a loss for words once being informed through an earpiece that he wasn't supposed to call Nitro, Roman is informed by Nitro that he set up the mistaken call, that his company bought out CSRN, and that Nitro fires Roman on the spot.
After the credits are finished, Knoxville will challenge the player to a dramatic High Stakes challenge, risking five gold from the player instead of the typical two, and his own Ferrari FXX K with unique livery.