I finally found them - Half Life 2 First time playing

[@ulisesbarrios3317]

While based on a generic scientist model, Alyx's dad actually "appeared" at the start of HL1.
Remember that scientist who operates a retinnal scanner right after the resonance cascade? It's pretty much asumed he's the same person, sending you up to call for help, as Eli states seeing Gordon the last time at BM in this chapter.