When the first Doctor regenerated into his second incarnation, it was a brand new idea and unlike anything we had ever seen before. The new Doctor was the same, but different!  He was wittier, more light hearted, but with a slightly darker side.  He was still brilliant of course, despite his bumbling outer appearance.  I sometimes wonder if he inspired the character of Columbo many years later.  Patrick Troughton was our Doctor from  November 1966 to June 1969 and appeared in 119 episodes.