Coming at this from the opposite direction, the first word I think of is artifex (-icis, m/f). It refers to a person who is highly skilled and knowledgeable about a specific topic, but not necessarily in a good way. An artifex is capable of twisting and controlling and manipulating something, whether it be marble and paint or the mood of a crowd.
Here's a positive example from Aeneid 1.455:
artificumque manus inter se operumque laborem
miratur, videt Iliacas ex ordine pugnas...
He sees the battles of Troy all in order, and marvels at the skill of the crafters and the effort of their works...
But it was also an epithet of Odysseus, for example, when Sinon is explaining how he was chosen as a sacrifice (2.125):
hic Ithacus vatem magno Calchanta tumultu
protrahit in medios; quae sint ea numina divum
flagitat. et mihi iam multi crudele canebant
artificis scelus, et taciti ventura videbant.
Here Odysseus brought out the seer Calchas among them, amid great commotion; he demanded to know from him what the will of the Gods might be. And already many people were cruelly predicting that schemer's wickedness, and were foreseeing what was about to come.
I hesitate to call it a real translation of "nerd", since it doesn't imply anything about social awkwardness—quite the opposite, in fact. But it's a word implying specialized skill or knowledge, which can either be a compliment or an insult depending on context.