William H. Trethewey

William Henry “Bill” Trethewey, 85, of Mt. Lebanon, Pennsylvania, passed away peacefully on Sunday, February 1, 2026, following a brief illness.

Born on August 16, 1940, in Gary, Indiana, Bill was the eldest of four children of William Arthur Trethewey and Elsa (Kokko) Trethewey. He spent his early childhood in Gary before moving with his family to Pittsburgh in 1948. That move eventually resulted in a proud family legacy in Mt. Lebanon, where Bill graduated from Mt. Lebanon High School in 1958, a tradition later followed by his five children and four of his grandchildren.

Bill earned a Bachelor of Science degree in Metallurgy from Grove City College, where he also served as President of his fraternity, Kappa Alpha Phi. He went on to receive his EMBA from the University of Pittsburgh. He built a distinguished career in the steel industry, beginning as a metallurgical engineer with U.S. Steel. Over two decades, he advanced into supervisory and production management roles before becoming Regional Sales Manager for Foote Mineral, specializing in technical metallurgical sales and solutions. He later served as Senior Vice President at Remacor, Inc. and ultimately founded his own consulting business. Though his life’s work centered on some of the world’s strongest materials, his greatest strength was always rooted in his family.

A gifted athlete from an early age, Bill once pitched a no-hitter in Little League and earned varsity letters in both basketball and baseball at Mt. Lebanon High School. He later became an avid runner and looked forward to the annual Pittsburgh Great Race. A lifelong sports enthusiast, he rarely missed a chance to watch his children and grandchildren (and their friends) compete, whether in Mt. Lebanon or across the globe. He was also a devoted fan of Pittsburgh sports, cheering on the Steelers, Penguins, and Pirates through decades of triumphs. He attended multiple Steelers Super Bowls and Pirates World Series games during the 1970s glory years and celebrated Penguins Stanley Cup runs with his family.

He became known as “GPa Bill” to many as his beloved wife of more than 50 years Sue cared for ninety children over 35 years, and he treated each as if they were part of his own family. He formed easy friendships everywhere he went from around town to the JCC, where he was a regular and often made “five-minute friends,” having conversations with whomever he found himself by. He was a natural teacher, always ready with life advice or encouragement. He valued education deeply and often reminded young people to be “student-athletes,” not the other way around.

Bill loved to travel and see as much of the country and world as possible. New England held a special place in his heart, along with Wyoming, Fort Lauderdale, especially the Lauderdale Yacht Club, the Canadian Rockies, Austria, Germany, and Italy.

Bill was preceded in death by his parents; his wife, Susan Hackenburg Trethewey; and his sister-in-law, Linda Trethewey. He is survived by his siblings, Tom Trethewey, Marty (Jeanine) Trethewey, and Liisa (Rick Reilly) Trethewey, along with many nieces and nephews.

He is also survived by his five children: Scott (Linda) Trethewey, Heather (Sam) D’Alesandro, Liz (Keith) Schmitt, Dick (Beth) Trethewey, and Bob (Kelly) Trethewey. Bill was the proud “GPa” of 17 grandchildren: Jack (Martha) Trethewey, Katie (Charlie) Arndall, Scott Trethewey, Daniel Trethewey, Anna D’Alesandro, Matt D’Alesandro, Megan D’Alesandro, Zac D’Alesandro, Katie Schmitt, Abby Schmitt, Max Trethewey, Ava Trethewey, Ben Trethewey, Greta Trethewey, Charlie Trethewey, Alex Trethewey, and Quinn Trethewey; and three great-grandchildren: Lily Trethewey, Rhodes Trethewey, and Charlotte Arndall.

Visitation will be held Friday, February 6, 2026, from 2:00 to 7:00 p.m. at WILLIAM SLATER II FUNERAL SERVICE (412-563-2800) 1650 Greentree Rd. Scott Twp. 15220. A funeral service will be held Saturday, February 7, 2026 at 3:00 pm at Southminster Presbyterian Church, 799 Washington Road, Pittsburgh, PA 15228. EVERYONE PLEASE MEET AT CHURCH. Burial will be private to the family. 

In lieu of flowers, memorial contributions may be made to Falcon Camp’s Decker Memorial Scholarship Funds, where 100% of donations support the endowment providing young people with meaningful camp experiences. Falcon Camp held a special place in Bill and Sue’s hearts, beginning when they met there as counselors in 1959 and continuing through generations of their family. www.slaterfuneral.com

Donations may be made by check payable to The Decker Memorial Scholarship Funds and mailed to: Decker Memorial Scholarship Funds, c/o James Mahen 7074 Timbercrest Way, Castle Pines, CO 80108

Online donations: https://www.paypal.com/fundraiser/charity/2403903