The Doctor has changed a lot from one incarnation to the next on Doctor Who. Each time they have regenerated into a new body, they have also gained a new personality, allowing the character to evolve and change over time. Across all of their incarnations, however, the Doctor has often faced difficulties in truly relating to their human companions. The Time Lord's fundamentally alien nature has always left humanity just beyond their reach. Still, some incarnations seemed less alien in nature than others. The Tenth Doctor, played by David Tennant, seemed particularly human for a Time Lord.
Source：https://www.cbr.com/doctor-who-tenth-doctor-human-explained/
