[Jorgen]

Snorlax 1st, Ttar 2nd sounds pretty good to me. Snorlax's peak is higher, and has consistent dominance through Gens 1-3, though Ttar's peak and consistency come awfully close. I'll agree with Borat that it isn't exactly "dominant" in GSC so much as it is a role player (albeit a versatile one).

As for #3 I'd have to go with Zapdos. In Gen 1 it honestly wasn't actually OU, though with Rocks gone it was still very effective. As for Gen 2 it is clearly #2 in the game behind Snorlax as a weird hybrid of offense and defense that could stay in against most things, force switches, and even bait and kill Snorlaxes with Thunder. In Gen 3, Zapdos runs into more STAB Ice Beams and Rock Slides and more need for different Hidden Powers, but it's still a great offensive defensive Pokemon that can tank and hurt most things. It also has a niche on BP teams as the 2nd strongest Pokemon (next to Celebi) with BP (plus Electric moves for wrecking Skarms). In Gen 4 it still maintains its presence as an offensive defensive hybrid, being able to force plays with its raw power while staying in against most anything thanks to its typing and solid all-around stats. This consistent presence and high peak in Gen 2 puts it very very close to Ttar, though Ttar peaks even higher and maintains a consistently strong presence otherwise to beat out Zapdos.

As for #4 I'd go with Gengar. A role-player in Gens 1 and 2, in the former as the fastest Sleeper and viable Exploder and the latter as an assassin that breaks walls with Explosion and surprises. In Gen 3 it started off as the premier wallbreaker with McGar and in modern ADV is the premier SpinBlocker and Special Attacker in the tier. A top 3 Pokemon in ADV for sure. As for DPP it falls off a bit with the ubiquity of Pursuiters (including ScarfTar which outspeeds it), though with Substitute or Protect it can play around them and wreak havoc with its newfound STAB with Focus Blast coverage.

EDIT: Actually on second thought, Celebi probably deserves the #3 slot. It was ultimately banned from GSC, though it was pretty ubiquitous before its ban. In a Celebi OU Celebi is clearly the #2 mon and Zapdos is nowhere near as good, having to run Thunder Wave + Drill Peck to stand a chance at killing it. In ADV Celebi is also a top 3 mon from what I understand. In DPP it's got a decidedly more mediocre showing though it's still relevant as a defensive Pokemon. Celebi never hits #1 and isn't quite as consistent as Ttar (as evidenced by its poorer DPP showing, which I'd reckon is less than Ttar's GSC showing as a widely-used Pursuiter that can also play other offensive and defensive roles competently, albeit with mediocrity), putting Celebi at #3. Zapdos and Gengar follow for 4th and 5th, respectively.