Star Trek: 15 Greatest Ever Time Travel Episodes
10. The Visitor - DS9
Though time travel episodes allow for comedic exchanges like in Little Green Men and adventurous ones in almost every other example, in The Visitor, it results in arguably one of the very most emotionally gut-wrenching episodes of Stat Trek ever.
It sees Captain Sisko become trapped in time (through some typical science jargon that really isn't important), and reappearing to his son Jake (who assumes him killed) throughout his life. Jake is haunted - both by his father physically and by his inability to free him from his time prison - and he devotes his life (to the detriment of his happiness) before realising the only way to free him is to kill himself.
It's a seriously well written episode, exploring death, grief and family through temporal fluctuations and the interactions between the ageing Jake and Sisko are really quite affecting.