The nine highlighted cells contain multiple letters: two or more letters from the down clue, and two or more letters from the across clue (where applicable). The letters in each of these cells anagram to a character that belongs to a certain group. Furthermore, nine clues contain an extra word – these words together form a cryptic clue for the group's name, which is the final answer (19 letters, four words).
Across
1. Revolutionary clergy without fashionable allure (9)
6. Interrupting period of growth, guy's at HR's lavatory (8)
9. Temporary trend to almost vanish (3)
10. A trip abroad regularly producing jewelry (5)
11. An African country, among others! (7)
12. 6 across, across the pond, or metro's body defaced (8)
14. Man next to tree at high altitude (6)
16. False deeds leading to verifiable evidence (5)
18. Asian people from Turkey's capital reformed Islam (6)
19. Part insect with snake (4)
22. Bathed before gym class and ultimately managed to be drowning in work (7)
23. Sandwich shop from Indian city called out (4)
24. Facing type of sound in mission as a loner (5)
26. Nosy animals eavesdrop US tax office (6)
27. Spy base compromised, primary defences being circumvented (8)
30. For example, a piece in a newspaper (7)
31. Musician's piano in support (5)
32. Product that's made from berries in Virginia (3)
33. A people of Asia's, containing fighting extremists! (7)
34. Dress a pole-dancing old pussy-cat (10)
Down
2. God possessed extremely loud engines (5)
3. Medium risotto mixed for driver (8)
4. Powerful case of singing about sci-fi film (6)
5. Sheep trimmer in Oregon revealed (6)
6. Cooking Gable's rolls (6)
7. Part of midterm in Alsace leading to finals (9)
8. Make fun of Nicolas's body part (7)
9. Insects recreated life inside sacks (9)
13. Broken US car brought in to Euro restoration (3,2,5)
15. Capturing one-time horror, moving gaily, showing dexterity (7)
17. Half of 34 across carried in broken cart to queen (9)
20. Partially help a lad injure a knight (7)
21. Unaltered single film I ignored (8)
25. Middle of kitchen counters showing fractures (6)
26. Country's temperature, cold precipitation and… (8)
28. … epic narratives described by leaders of South African state (5)
29. Girls supporting Mr. Franklin's Ohio team (7)
31. Christopher's ship produced by a group leaving Mexican party item (5)