As a child I recall seeing a picture of the Second Doctor grimacing in a newspaper or magazine and I was actually a little frightened! Over time I have developed a deeper appreciation for earlier stories and in particular, the Second Doctor and his era.
Before The Doctors initial regeneration, he was perceived as a very austere gentleman and although people didn't always see it he did have a twinkle in his eye, a sense of humour and a sense of adventure. When he regenerated, the younger looking Doctor let all of this energy and mischief take centre stage, but did not forget his manners and his sense of justice.
Perceived as a clown, a buffoon who didn't seem to know what he was doing. This new tact the Doctor adopted worked well to deceive his enemies, although he was clever enough to make it difficult to differentiate from when he really didn't have a clue and was buying time to solve the predicaments he faced. He always had a tune to play on his trusted recorder, a little dance or a joke to share.
However, the Doctor had not forgotten his more serious side. He still challenged authority ferociously, despised technology (especially computers, in The Invasion) and scorned those who were causing unnecessary suffering, or choosing a path of selfishness.
He still cared for the human race, although it still exasperated him greatly. He remained a protective figure to his companions and became racked with guilt if any of his actions put them into danger. The scene in Tomb of the Cybermen when he talks to Victoria about family was a particularly poignant moment.
His intelligence was still going strong despite initial appearances. One particular example of this at its very best was in The Mind Robber where he uses his raw knowledge and emotional intelligence to try and prevent manipulation, to maintain control within in a fictional world of potentially dangerous imagination.
Every time the Doctor regenerates we see the same character traits in varying concentrations. The Cosmic Hobo for me is the definitive. His energy, his child like wonder and glee, his dislike of authority, his playfulness, the sparkle in his mischievous eyes, his empathy, and his stubbornness. The Charlie Chaplain Time Lord with two very big hearts of gold.