1. Eccleston's Departure: Christopher Eccleston, the Ninth Doctor, had decided to leave the show after one series. This opened the door for a new actor to take on the iconic role.
2. Russell T Davies' Vision: Russell T Davies, the showrunner at the time, had a specific vision for the new Doctor. He wanted someone who was charming, charismatic, and able to convey both a sense of vulnerability and strength.
3. Tennant's Previous Work: Davies had been a fan of Tennant's work for a while, particularly his roles in plays like "Hamlet" and "Much Ado About Nothing." He also appreciated Tennant's comedic timing, as seen in his roles in shows like "Casanova" and "Black Books."
4. The Casting Process: The casting process was quite extensive, with many actors auditioning for the role. Tennant, however, wasn't initially on the shortlist. He was filming a film at the time and only became available later.
5. "The Test" and the "Second Choice": When Tennant finally auditioned, he impressed Davies and the producers with his performance. His audition was so strong that he was immediately considered a frontrunner. However, the producers initially offered the role to another actor, who declined.
6. Tennant's Acceptance: With the other actor turning down the offer, the producers approached Tennant again, and this time, he happily accepted.
7. A Legacy Made: Tennant's portrayal of the Tenth Doctor proved to be a massive success. He became one of the most popular Doctors ever, bringing a new level of energy and emotion to the role.
So, it wasn't a smooth, linear path for Tennant to become the Tenth Doctor. It was a combination of timing, talent, and a bit of luck that ultimately led to this iconic pairing.