I was probably 8 years old when I first came across Dr Who. Patrick Troughton (the second doctor) was just about to leave, and the dynamic dandy, Jon Pertwee, was about to begin his tenure. To see the doctors in their chronological order, click here. I was only 2 years old when William Hartnell became the first 
doctor and it wasn’t until I was 7 or 8 that I came across Dr Who in a comic. At that time, I was introduced to Patrick Troughton, with companions, Jamie (Frazer Hines) and Zoe (Wendy Padbury). However, it was a while before our family had even a black & white television, and I only recall seeing one episode featuring Patrick Troughton, before Jon Pertwee took over, in 1970. I was now age 9. For me, age 9 in children is possibly the peak time for achieving greatest interest and creativity, in the world around you. Dr Who could not have come at a better time and inspired by Jon Pertwee, my interest in science and adventure expanded and flourished. Many Dr Who stories were played out, with the assistance 
of my younger brother, who alternated between being ‘the Brigadier’ – Brigadier Alistair Gordon Lethbridge-Stewart (Nicholas Courtney), Captain Mike Yates (Richard Franklin), or the Doctor’s greatest adversary, ‘The Master’ (the fabulous, Roger Delgado). Sadly, Roger Delgado died in 1973, and many believe this was given as a reason by Jon Pertwee, a close friend, as to why he left the show, a year later. (Wikipedia history of Jon Pertwee).
Jon Pertwee had three companions, at different times of his role as Dr Who: Elizabeth “Liz” Shaw (Caroline John); Jo Grant (Katy Manning); and Sarah Jane Smith (Elisabeth Sladen). As well as my younger brother, I also had a younger sister, who by the time Jo Grant came along, was able to play her in our childhood games of Dr Who.
Also, age 9, I went on a school holiday to Wales. The friend I was sitting with on the bus was reading a Dr Who book: ‘Dr Who in an Exciting Adventure with the Daleks’ by David Whitaker – Armada 1965. We must have started talking about Dr Who and he suddenly passed me the book and said, “you can have this.” It was the first Dr Who book I’d come across and although it was pre-Jon Pertwee, I read it with great enjoyment. By the time Jon Pertwee was a couple of years into his tenure, I had a small collection of contemporary Dr Who books, featuring Jon Pertwee’s doctor.
(As a child, I used to play Dr Who with my younger brother. I also managed to find a blue crystal, to re-enact scenes from the programme).
It would be amazing enough for a person to have one successful career, but Jon Pertwee excelled long before he went into acting and media. He was a senior intelligence agent during the Second World War and reported directly to Winston Churchill. And after Dr Who, and a number of Radio shows, such as ‘The Navy Lark’*, became famously associated with Worzel Gummidge. Read the article below:
Jon Pertwee: From Secret Agent in WWII to Dr Who (pdf)
See old photographs of behind the scenes third Dr Who at the BBC in 1970
*Jon’s distant cousin, Bill Pertwee (famous as the Chief ARP Warden, Hodges, in Dad’s Army, also featured in the Navy Lark.