How would you say this? Praterita defensor? Something like that? I want to be able to say, in Latin, 'defender of the past', in the same way one would say 'fedei defensor'.
Laudator temporis acti, from Horace's Ars Poetica (line 173), "a praiser of times past," might not be what you want, since the intended meaning is pejorative, but I offer it here because whatever phrase you do settle on should be chosen with knowledge of this phrase and the meanings it carries.
Multa senem circumveniunt incommoda, vel quod
quaerit et inventis miser abstinet ac timet uti,
vel quod res omnis timide gelideque ministrat,
dilator, spe longus, iners avidusque futuri,
difficilis, querulus, laudator temporis acti
se puero, castigator censorque minorum.
Many ills encompass an old man, whether because he seeks gain, and then miserably holds aloof from his store and fears to use it, or because, in all that he does, he lacks fire and courage, is dilatory and slow to form hopes, is sluggish and greedy of a longer life, peevish, surly, given to praising the days he spent as a boy, and to reproving and condemning the young. (tr. H. Rushton Fairclough)
The tempus actum that Horace was referring to was the boyhood of a cranky old man, but the phrase has come to mean one who defends past periods of history, before the defender's own life, as superior to the present, at least in some ways. For example:
[T.S.] Eliot stood—as he once famously said of himself—for conservatism in politics, classicism in literature, and Catholicism, or rather Anglo-Catholicism, in religion. He looked back into the past, the mediaeval past, as a confirmed laudator temporis acti and in the mediaeval past he looked back not only to John Donne among the metaphysical poets, nor only to William Shakespeare among the Elizabethan dramatists, but before them to the great Dante among Italian poets and behind Dante, though not so obviously, to St. Thomas Aquinas among the scholastic theologians. (From "T.S. Eliot's Metaphysics" by Peter Milward, Culture and Civilization 2009.)
That is how the phrase is often used: ironically evoking the crankiness of Horace's original, to mean that the laudator is actually wise to uphold virtue from previous historical periods now mostly forgotten. Another illustration is the title of the blog Laudator Temporis Acti, by Michael Gilleland, who calls himself an "antediluvian, bibliomaniac, and curmudgeon".