Lieutenant Gaines is the Enterprise-D officer at tactical during parts of the present-day timeline in All Good Things..., the final episode of The Next Generation.
Gaines appears in All Good Things... While Jean-Luc Picard slips between three periods of his life, the events of 2370 take the Enterprise to the Devron system in the Neutral Zone, where a spatial anomaly has appeared.
Gaines stands at the tactical station on the bridge in this timeline, reporting on the Romulan warbirds gathered at the border and on the anomaly itself as Picard negotiates with Tomalak for permission to send one ship from each side to investigate.
The character is a small part of the series' last hours, one of the junior officers who keep the bridge running while the senior staff try to understand why their captain is jumping through time.