There are many heroes within the Star Trek franchise, from life-saving captains who swoop in to save the day, to mere civilians who take up arms to defend others and do the right thing. But among these, the bravest are the people who chose to sacrifice their own lives (and often the lives of their crew) in an attempt to save total strangers. In this bracket of heroes is Lieutenant Richard Castillo, helmsman aboard the USS Enterprise-C, who played a vital role in ensuring long-lasting peace in the Alpha Quadrant.
Castillo’s story features in the critically acclaimed The Next Generation episode “Yesterday's Enterprise.” The episode's story helped fill in some gaps between The Original Series and TNG, especially in relation to the ending of the war between the Federation and Klingon Empire. The Enterprise-C, commanded at this time by Captain Rachel Garrett, went down in history as the catalyst which stopped the fighting — largely due to the actions of Lieutenant Castillo.
In 2344, the ship responded to a distress call from a Klingon outpost that was being attacked by the nefarious Romulans. The history books told that they defended the outpost for long enough for the Klingon civilians to evacuate, but in the process were destroyed by the Romulans. Their sacrifice caused negotiations to open up between the Klingons and Federation. The Klingon empire saw the sacrifice as an act of unbelievable heroism and honor, something they never expected from humans, and chose to return the favor.
While this is the official story, "Yesterday's Enterprise" reveals that there was more to this story. While under attack from the Romulans, the Enterprise-C was badly damaged, but managed to evade long enough to drift into a temporal rift in time, transporting them all the way into Jean-Luc Picard's path in the 24th century. While the time was right, and the crew looked right (at first), something was off. This was not the 24th century audiences were used to. For starters, Tasha Yar was still alive, and was at her post as chief tactical officer. It turned out that when the Enterprise-C came through the rift it altered the timeline, causing them to have never been destroyed by the Romulans protecting the Klingons. As a direct consequence, the Federation and Klingon Empire were still at war all these years later.
Things were apparently bad for the Federation. The Klingons were on the brink of winning, and Starfleet was all but crippled from the constant onslaught. While the episode focuses a lot on the alternate timeline, war, and the options they all have to return everything to the correct reality, it also focuses on Yar and a certain Lieutenant Richard Castillo. He was the helmsman aboard the Enterprise-C, and was on the bridge during the original firefight that damaged the ship and sent them through the time rift. In that battle, his captain was badly hurt and put in sickbay, where she remained for the majority of the episode. This resulted in Castillo being the main liaison between his crew from the past, and the alternate reality crew of the present. While on board the iconic Enterprise-D, his ships' successor, he grows close with Yar. She teaches him all about the amazing technological advancements they have made over the years, and what life is like for them all in the 24th century.
As the episode continues, the threat of the Klingon empire winning looms over them all. Together they discover that there may be a way to stop it, and return themselves to the correct timeline where peace between the two races had been achieved. All this came at a great cost, however: the Enterprise-C would have to return through the time rift and be destroyed by the Romulans, causing events to happen as they should and peace to be brokered. It was a huge request to make of these people, traveling back to their inevitable death to save countless lives. Yet, Captain Garrett and Castillo decide it is necessary. Many of the crew agreed, pinnacles of heroism, and they agreed to return, a decision that caused distress for both him and Yar. Despite this, they knew it was the right thing to do.
With everything set to go, a Klingon bird of prey appeared out of nowhere, attacking the Enterprise and resulting in Captain Garret's death. Castillo, the next-highest ranking officer for the Enterprise-C, stepped up and took command. He followed through with his late captain's wishes, and prepared to go through the time rift. While this was happening, Yar discovered that she was not part of the prime timeline in the 24th century, and that she had died years ago in a meaningless and utterly untimely way. She decided she would rather go with Castillo, so her death would actually mean something. He welcomed her, and together they traveled back through time to their deaths, knowing that their sacrifice would return the timeline to normal and stop countless lives from being destroyed. Not only did this episode show the heroism of Castillo, a name lost when time reverted to its correct reality, but it also gave Yar the send-off she always deserved.