“Tom Baker and The Doctor was the single best marriage of an actor to a role in TV history,” Russell Davies [21st-century Doctor Who producer] said.
The fourth doctor at tardis wikia.
"You may be a doctor but I'm the Doctor, the definite article you might say."
―The Fourth Doctor to Harry Sullivan
Ranking of Dr. Who doctors
1. Tom Baker (fourth)
2. David Tennant (tenth)
3. Jon Pertwee (third)
7-10. Irrelevant: Too large a drop in quality to care
Doctor Who Companion at wikipedia
Ranking of Companions
1. Sarah Jane Smith
4. Martha Jones
5. Captain Jack Harkness
7-9. Adric/Leela/Donna Noble
10+. Irrelevant: Too large a drop in quality to care
Brigadier not officially a companion but I would put him 6th ahead of K9's.
Nicholas Courtney played the Brigadier and was to record but had to be replaced for health reasons. If there are more audio recordings he could record them.