Here we are with third Doctor, John Pertwee.
This time I could show his first apparition with regeneration.
John Pertwee got several records: he was the first Doctor in color, the first who had his episodes totally kept in the archives and, at that time, the more long-lived with five seasons (the record was then broken by his successor Tom Baker, a record which still resists).
This is what is commonly called a "UNIT-story", where the Doctor acts as scientific advisor of UNIT (United Nations Intelligence Taskforce), the organisation led by brigadier Lethbridge-Stewart (Nicholas Courtney).
The Doctor has no choice: the Time Lords have tried him (in the last Patrick Troughton story, "The War Games"), forced to regenerate (simply to allow Troughton to be replaced by Pertwee), and exiled on Earth, with the TARDIS grounded.
UNIT-stories, as said, were typical of the third Doctor (so much that Pertwee left the show when it was decided to abandone them), anyway thi sin't the first at all.
In fact Lethbridge-Stewart (then colonel) had already appeared in the Troughton episode "The web of fear", and there he was convinced to found UNIT to protect mankind from aliens.
And UNIT's first apparition, led by now-brigadier Lethbridge Stewart, was in "The invasion".
In both episodes the brigadier faced the second Doctor, so, knowing nothing about the Doctor's power to regenerate, is quite puzzled when he finds a man never seen before who pretends to be the Doctor.
He will be more used to that in the episode "Robot", when he will see Pertwee regenerating again and becoming Tom Baker.
Playing the brigadier, Nicholas Courney is the most long-lived supporting charachter in "Doctor Who": we see him in "The web of fear" in 1968, then 9 months later in "The invasion", and in this episode in 1970 he entered in the regular cast.
The last but one "UNIT-story" is "The android invasion" in 1975, with Tom Baker.
The very last is "Battlefield" in 1989: there is the seventh Doctor Sylvester McCoy, we are in the last "classic" season and the brigadier is now 60 and retired... but it's not yet the end.
UNIT is mentioned in "Aliens of London", an episode with the ninth Doctor Cristopher Eccleston; then the brigadier appears (near 80) for a brief cameo in an episode of "The Sarah Jane adventures", a spin-off where Sarah Jane Smith (Elizabeth Sladen), former companion of third and fourth Doctor, too struggles against alien invasions...
In a nutshell, the character popularity continued during the years, and we can't see him more often probably for age limits...
Now let's go to the story. Strange meteorites, hollow and apparently made of plastic, fall on Earth, and UNIT investigates. The TARDIS too materializes, and a never seen before man is found unconscious near it. The brigadier is puzzled: he doesn't know that the Doctor has the power of regenerating his body, and has just regenerated...
WARNING: to read the comic you need Acrobat Reader.
SPEARHEAD FROM SPACE Part I - Part II - Part III - Part IV