Multiple realities
(covers information from several alternate timelines)

Ensign Fletcher was an engineer serving aboard the USS Enterprise-D during the 2360s through the early 2370s.

Fletcher was already aboard the ship on its maiden voyage to Farpoint Station in 2364 and among the crewmembers who welcomed Captain Jean-Luc Picard on board in the shuttlebay.

In the anti-time past, Fletcher was supposed to get Lee and Munoz down to main engineering to realign the power grid. (TNG: "All Good Things...")

When Geordi La Forge suddenly felt dizzy due to a temporal anomaly distorting his VISOR in 2368, Fletcher was able to grab him before he could fall down from the catwalk to the bottom of the warp core. (TNG: "Cause and Effect")

In 2370, during a crew evaluation report, Counselor Deanna Troi and Commander William T. Riker discussed the merits of promoting Carstairs or Fletcher into a supervisory position. Although Fletcher had more experience with propulsion systems, Troi favored Carstairs for her people skills. Riker went with Troi's suggestion. (TNG: "Lower Decks")

Fletcher was played and voiced by an unknown actor in "All Good Things...".