Trevor West (God rest his soul) born in 1957 is the deceased father of Stacey and Jason, brother of Bryn, and husband of Gwen. He died about a year or two before the series begins.
Trevor was popular and well thought-of by those who knew him, despite their anecdotes about him suggesting that he was a problem drinker with a hair-trigger temper who resented having to take responsibility for his children - especially his first, Jason (though he seems to have been better-disposed toward his second child, Stacey).
He died after an illness which gave him time to reflect on his relationships, and he left a heartfelt letter to Stacey which Bryn passed on to her on her wedding day.
There is deleted scenes of Stacey, Gwen and Bryn visiting Trevor's grave in a Cemetery in Bridgend. The scenes were meant to be aired on Series 1 Ep 5.