See, now, THIS is the sort of thing where my memory for miscellaneous trivia really comes in handy... I can remember the order of most of the sets I got, honestly.
Long post incoming.
My very first was Onua Mata, back in January '01. Lego World Club magazine had presented me with not only a full double-page-spread of all six Toa but also a separate comic starring Kopaka. Between the fact that they looked kinda like Slizers, who I had become a fan of not long before, and the intriguing story and designs, I was hooked. Although, I will admit, there was one reason and one reason only why I chose Onua as my first Toa over any of the others: because, from his main picture, I could not figure out quite how his anatomy worked and I wanted to resolve that puzzle. I got him from out (now long-gone) local toy and model shop, after school the following day.
Continuing into '01; my second was Turaga Vakama, I don't remember the context in which I got him. Third and fourth, come closer to summer, were Pohatu and Tahu, in that order, who I both got on a trip to Torquay - Pohatu at a service station on the way, Tahu from Woolworths once we got there. A whole load of my Bionicle sets came from various Woolworths' stores for that matter... that chain is still missed. In any case, I later in the year got Kopaka for... Christmas, I think? Then Gali in the after-Christmas sales.
For 2002... I didn't, initially, intend to buy any of the Bohrok, they didn't particularly interest me; however, my local Woolworths (any bets for how many times I'm gonna mention that chain in this post? xD) had Bionicle sets on a Buy-One-Get-One offer; so when I grabbed Lewa to complete my Mata collection, I took advantage of the offer to pick up Tahnok too. '02 didn't see me buy many other Bionicle sets; only the Boxor, with money I got for my birthday when October rolled around, and Kopaka Nuva from that year's Legoland trip. Over the course of the following year, I would pick up the rest of the Nuva too.
My first sets of 2003 were Nuhvok-Kal and Lehvak-Kal. For reasons I'm still not quite sure I can explain, the Kal appealed to me far more than the traditional Bohrok; perhaps because of their silver colour schemes, or because they were individual entities rather than just one of a swarm. I don't quite remember which order I got those two Kal in, but I know for sure that the first one I got in a buy-one-get-one offer with Tahu Nuva (Woolworths again!), while the other was an Easter present. Following on from that, I grabbed Matoro, Kopeke, Hewkii and Hafu all at once when they came around - I have always had a soft spot for the Mata Nui Matoran - and, subsequently, both Takua & Pewku and Jaller & Gukko, as quickly as I was able to save up the money to afford them. Takanuva, Macku, Hahli and Panrahk were all birthday gifts... and, aside from rounding off my Toa Nuva collection, that was it for that year. The rest of the sets would be picked up at various later dates over the following years.
2004 was the first year where it, somehow, became a goal of mine to collect every single set. My first were Toa Whenua and Ahkmou, who I bought on a Legoland trip early in the year, and in short order picked up the rest of the Metru and Matoran locally... Vhisola, I believe, being second; then Onewa; Nuju, Ehrye and Tehutti all together; Vakama and Nuhrii; then Nokama, then Orkahm. Matau was the last, and by that time I had already picked up my first Vahki, Keerakh. They would be followed, not too long after, by Turaga Dume; and then, Vahki Zadakh and Bordakh. A second Bordakh, as well as Nurakh and Rorzakh were added in short order as birthday presents from my school friends; Krekka was picked up on a trip up to the Blackpool Illuminations in the November. Toa Lhikan only appeared a few days before Christmas, and was eagerly snatched up as soon as he appeared; Vorzakh was collected in the after-Christmas sales; and Nidhiki was very much an illusive final piece, the search for him taking me around several local towns with no success before my parents let me buy him off Lego Shop@Home instead.
2005 started off with the Rahaga - five of them sold together in a lot (Pouks was absent) by Argos, a few weeks before their actual UK release date. Oonhurak and Keelerak followed along as that year's Easter gift, I think Pouks, then Keetongu, came not long after... and then I kind of fell off the Bionicle fandom for the rest of the first half of the year, as the Revenge of the Sith hype consumed all my interest. Even after the movie came out, it took my ages to return my attention to Bionicle - though I did still pick up the Visorak Battle Ram playest during that time, if memory serves - and that was only achieved when the Toa Hordika finally made it to the UK and I snagged up Matau first. Toa Iruini would follow, as would Onewa Hordika and Toa Norik; the Battle for Metru Nui playest was my birthday present that year; then came Whenua and Sidorak, together, in pre-Christmas sales; and finally Roodaka was found just before the end of the year.
For 2006, Garan and Kazi, bought together, were my first. Then Reidak, who turned up in a different Woolworths a handful of days before the Piraka's projected UK release date; Brutaka, I believe, was next, then Thok - though not sure if he was after Balta and Dalu, or before - and was followed, over the next while, by Piruk, and then Velika. This, too, was the year I discovered eBay, from where Avak was purchased as Summer approached; and Axonn was somwhere in amongst those, too, though I forget exactly where. That year's summer holiday saw me pick up Vezon and Fenrakk from my first trip to an official Lego store, and five out of six Inika were picked up over the course of the rest of the year. (In order: Nuparu, Hewkii, Jaller, Matoro and Hahli. Not intentionally the exact same order I'd got the original Mata in, but that was the way it panned out.) Hakann, Vezok and Zaktan were grabbed from eBay too, just before Christmas (at the same time as some surprisingly cheap '01 Rahi), and The Race for the Mask of Life playset, too, was scooped up in the post-Christmas sales.
2007's start was Kalmah, though not entirely by choice; he was the only one that Argos had in stock, and he was followed in short order by (and this may not be the exact order, but it's close) Dekar, Pridak, Defilak and Morak. Mantax and Carapar both came around Easter time (one of them was an Easter present, but I forget which); and Ehlek and Takadox, if I remember correctly, were both grabbed during a trip to visit my grandparents in Scotland, along with last year's Umbra. Again, my interest in Bionicle waned in favour of Star Wars for most of the summer, only returning with the Mahri, of whom I captured Kongu first... a choice dictated by the fact that he was the only one I (still) didn't have the Inika version of. He would be followed by, in rough order, Gadunka; Hewkii and Hydraxon; and Lessovikk. Karzahni and Thulox were both birthday gifts, and Maxilos was bought subsequently with an Amazon voucher (for literally his EXACT cost) I got for the same birthday. I had intended to leave my Mahri collection there, satisfied with just the two; but Matoro's in-character sacrifice abruptly changed my mind when the comic was posted here on BZP, and I'm pretty sure I made it my top priority to add him to my collection due to that. Jaller, too, would follow not much later.
And 2008 was entered with Pohatu Phantoka, Antroz and Icarax, all at once... I had Christmas gift money to burn, and, not expecting so see them all in one place on a trip to the Toys R' Us in Bristol, kind of splurged. I was somewhat more controlled after that, picking up Tanma, Kopaka, Vamprah, Gavla, Toa Ignika, Mutran & Vican, and finally Lewa only rather more intermittantly as the year progressed. My interests took another major shift in the summer of this year - towards, to my great surprise at the time, The Lion King of all things - but I was still determined to gather Bionicle sets all the same. Onua and Gali, together, were my first of the summer wave, followed by Takanuva; then Bitil, Tahu and Vultraz (the Woolworths chain was going out of business, and their closing down sale had all toys on buy-two-get-one-free offers, otherwise I may have been more restrained. MAY have), and later, Gorast. Mazeka was a birthday gift, the Rockoh a Christmas one, and Chirox was nabbed from BZP's own Buy-Sell-Trade forum just before the year closed... more to justify the shipping costs involved in grabbing a cheap Mctoran Kongu and a couple of other pieces we'd never got in the UK, than any other reason.
2009 was where I really started to wind down. Bara Magna didn't hook me, and while at first my intention was to give at least a few of the sets a chance... my first purchase, Fero & Skirmix, killed that intention pretty quickly. They weren't a bad set, but they were, to me, just... boring. Of the 2009 sets, all I picked up subsequently was Attakus (second-hand from a car boot sale), Click (free with The Legend Reborn DVD) and Kiina... whose unique design interested me, but didn't re-inspire me. Eventually, I would get my hands on Glatorian Mata Nui, too... many years later, by which point I was thoroughly underwhelmed by him xD
And 2010... Tahu Star. And Only Tahu Star. My interests were elsewhere, it was only the nostalgia that let me go as far as getting him at all!
And then, finally... Lewa Uniter, my only Gen 2 set, who I got just a month or two ago, as a reward for participating in last year's BZP fanfic exchange ^^
That isn't... my whole collection listed, of course. Most of the ones who I only picked up in subsequent years to their release, I don't remember exactly when they fitted in. I could tell you, for instance, the exact order I aquired the other five Bohrok from, and from where I got them, but I don't remember when their purchases actually took place, other than between 2006 and 2008. Same with many of the others I got only after their release years had passed.
But, haha, this was a memory trip, for sure! This, right here, is the kind of useless knowledge that my mind never lets go of xD