William Hartnell portrayed the 1st incarnation of the Doctor. He was not the best Doctor. Hartnell was the oldest actor who portrayed the Doctor. He was 55 when he got the part. Jon Pertwee was the 2nd oldest actor who portrayed the Doctor. Pertwee was 50.
Hartnell starred as the Doctor in 29 episodes. After three years of portraying the Doctor, Hartnell was replaced because he was getting too ill to continue playing the role. He was replaced by Patrick Troughton.
I give William Hartnell a 3 star rating.

My least favorite:  old, cranky, and not very interesting.