Miles O'Brien

At first he didn't even have a name.  Colm Meaney debuted in "Encounter at Farpoint," the pilot episode of Star Trek: The Next Generation.  He didn't appear again until "Lonely Among Us," but was again absent until the second season, when O'Brien became a more regular presence.   He became known as the transporter chief, and then got a wife, Keiko, and then a daughter, Molly.  If anyone's life truly progressed in Next Generation, it was O'Brien's.  He became the show's most regular supporting character, but didn't become a series regular until Deep Space Nine launched and he joined the new show's cast in the pilot, "Emissary."

I ranked him seventh in my list of Star Trek's 50 best characters, yet in many ways Miles O'Brien may be the best of them all.  He's arguably the most human, certainly the most humble.  He could have been a mild Irish caricature, the way Scotty was for the Scottish, but O'Brien made his mark on his own merit.  While Meaney himself started making a film career starring in Irish films, O'Brien proved to be the consummate Starfleet crewman (enlisting rather than becoming an officer like most Star Trek characters), tackling the tough task of cleaning up after the Cardassians to get Sisko's new station in working order.  He fit in as a member of two different casts, arguably more naturally than Worf.  The only inexplicable thing about O'Brien is that he never appeared in a Star Trek movie.  Of course, he might say that becoming best friends with Julian Bashir was more inexplicable, at least initially.

Next Generation appearances:

1. "Encounter at Farpoint" (1x1/1x2)
2. "Lonely Among Us" (1x7)
3. "The Child" (2x1)
4. "Where Silence Has Lease" (2x2)
5. "Loud as a Whisper" (2x5)
6. "Unnatural Selection" (2x7)
7. "A Matter of Honor" (2x8)
8. "The Measure of a Man" (2x9)
9. "The Dauphin" (2x10)
10. "Contagion" (2x11)
11. "The Royale" (2x12)
12. "Time Squared" (2x13)
13. "The Icarus Factor" (2x14)
14. "Pen Pals" (2x15)
15. "Q Who" (2x16)
16. "Up the Long Ladder" (2x18)
17. "Manhunt" (2x19)
18. "The Emissary" (2x20)
19. "Shades of Gray" (2x22)
20. "Evolution" (3x1)
21. "The Ensigns of Command" (3x2)
22. "The Bonding" (3x5)
23. "Booby Trap" (3x6)
24. "The Enemy" (3x7)
25. "The Price" (3x8)
26. "The Hunted" (3x11)
27. "A Matter of Perspective" (3x14)
28. "Tin Man" (3x20)
29. "Hollow Pursuits" (3x21)
30. "The Most Toys" (3x22)
31. "Sarek" (3x23)
32. "Transfigurations" (3x25)
33. "The Best of Both Worlds" (3x26)
34. "The Best of Both Worlds, Part 2" (4x1)
35. "Brothers" (4x3)
36. "Family" (4x4)
37. "Remember Me" (4x5)
38. "Legacy" (4x6)
39. "Data's Day" (4x11)
40. "The Wounded" (4x12)
41. "Clues" (4x14)
42. "Night Terrors" (4x17)
43. "Half a Life" (4x22)
44. "The Mind's Eye" (4x24)
45. "In Theory" (4x25)
46. "Redemption II" (5x1)
47. "Darmok" (5x2)
48. "Disaster" (5x5)
49. "The Game" (5x6)
50. "Power Play" (5x15)
51. "Realm of Fear" (6x2)
52. "Rascals" (6x7)
53. "All Good Things..." (7x25/7x26)

Deep Space Nine notable appearances:

1. "Emissary" (1x1/1x2)
2. "Captive Pursuit" (1x6)
3. "The Storyteller" (1x14)
4. "In the Hands of the Prophets" (1x20)
5. "Armageddon Game" (2x13)
6. "Whispers" (2x14)
7. "Paradise" (2x15)
8. "Crossover" (2x23)
9. "Tribunal" (2x25)
10. "Destiny" (3x15)
11. "Visionary" (3x17)
12. "Through the Looking Glass" (3x19)
13. "Explorers" (3x22)
14. "Hippocratic Oath" (4x4)
15. "Hard Time" (4x19)
16. "The Ship" (5x2)
17. "The Assignment" (5x5)
18. "The Begotten" (5x12)
19. "Empok Nor" (5x24)
20. "Honor Among Thieves" (6x15)
21. "Time's Orphan" (6x24)
22. "Prodigal Daughter" (7x11)
23. "Extreme Measures" (7x23)
24. "What You Leave Behind" (7x25/7x26)