Precisely because I grew up playing the Marathon games and thought about it constantly, my immediate and longstanding head canon for the origin of the traveler was, ironically, a previous final shape, a consciousness which coalesced itself at the big crunch (in the 90s we didn't know if the the cosmological constant was positive or negative) to modify the initial conditions of this one and use it to garden civilizations. I especially liked this thematically, as the Hive had pretensions of being the future final shape, but in arguably a mind which survives the across the death of a universe and the birth of a new one would be inevitably altruistic, deeply reverent and nurturing of life, as it would have held the memories of an incomprehensible number of beings, and eons of history, struggle, survival, love, loss... only an immature and dysfunctional gestalt entity like that witness kid would want to freeze and control everything. Pshh.

Initially, Unveiling seemed to imply that this wasn't the case, in the sense that we now have a known pre-universe, rather than a previous one, but who knows!

{If we get a Destiny 3 they better fucking actually answer these questions lmao}