Leon Vance NCIS
He is named Director after the death of Jenny Shepard. It has been revealed in the episode Knockout that he was originally from Ohio, but grew up in Chicago where he trained to be a boxer. In this episode, his wife stated that Vance attended the United States Naval Academy and was commissioned as a 2nd Lieutenant in the Marine Corps, but was forced to take a medical discharge before ever serving due to having undergone surgery to repair a detached retina suffered during his boxing career.
However, at the end of the episode, Ducky reveals to Gibbs that Vance's close, childhood friend who had died just prior to the start of the episode also suffered a detached retina. In the course of this episode, Vance also revealed that it was this friend who decided that Vance leave Chicago while the friend stayed behind. Vance said this despite his insistence to Gibbs that his friend was a Marine though there was no record of his friend's service in the military.
In 1991, just prior to joining NCIS, Vance was a student at the United States Naval War College in Rhode Island. His coursework at this time included Combat Philosophy and Advanced Cryptography.
Notably, Vance took over for Jenny Shepard during her leave of absence between Internal Affairs and Judgment Day, establishing himself as a formidable presence with Gibbs and his team. He and Gibbs clash during this span, prompting a cold war between them which ends with a détente between the two of them in "Agent Afloat" at the start of the sixth season; however, the two of them clash later on, as Gibbs feels he cannot fully trust Vance, though he cannot identify a specific reason why. Vance spearheads the investigation into Jenny Shepard's death, and is angered greatly when he is not kept in the loop by Gibbs and Mike Franks, who ultimately manipulate the situation to exonerate Shepard from her past failure, not what Vance had in mind. After Shepard's death, and possibly before, he lobbies the Secretary of the Navy hard to take over NCIS, as told in Cloak, but in Semper Fidelis the Secretary of the Navy informs Gibbs of a major operation which will require Vance to serve as its head, and that NCIS and the Navy will need Gibbs and Vance to get along, to which Gibbs is not comfortable but appreciates the situation.
Things come to a head in Aliyah, when Gibbs accuses Vance of selling out his team to Mossad Director Eli David, to which Vance responds that Ziva was a plant, used to get Mossad a foothole in NCIS through Gibbs. After this, the two of them realize that circumstances will prove one of them right. At the start of the seventh season, Vance approves Ziva's transfer to NCIS, proving that Gibbs was right, and Ziva was loyal to NCIS. Despite his professional attitude towards Gibbs's team, he shows that he does care about them at least once when Alejandro Rivera threatens Abby in "Spider and The Fly". He tells Alejandro to leave before he gets hurt and when Alejandro asks by who, he replies angrily: "By me."
Even after the events of Aliyah, Vance has been shown to still be in official contact with Eli David in David's capacity as Director of Mossad. This is shown when he receives a text message on his phone from Eli which says only: "I found him". Vance also refuses to discuss an Eli-phone call with Gibbs, despite knowing how dangerous Eli is, and his precarious relationship with Gibbs and his team.
Upon being promoted to the director's position at the end of Season 5, Vance immediately goes to former Director Shepard's office, and is seen to shred a single mysterious document from his own personnel file. It is later revealed in season 6 (Semper Fidelis) that the document was written by his supervising agent at the time. The Secretary of the Navy tells Gibbs that the file is a fabrication and that he thought all copies had been destroyed. It is further revealed in the season 8 episode, Enemies Domestic, that the head of the San Diego field office, when Vance was assigned there, had begun creating a legend for Vance that incorporated fictitious information about Vance in order to backstop a deep cover assignment, including the false information that Vance had been a pilot and director of a field office.