The "Stand By Me" actor died of a drug overdose on Oct. 31, 1993, at 23 years old
River Phoenix's sister is paying tribute to the late actor on what would have been his 53rd birthday.
One snapshot showed a black-and-white photo of River holding his hands to his head, while another showed an undated throwback image of the two siblings during their childhood.
"Happy birthday River," Rain, 50, wrote in the caption to her post.
"Happy birthday to your beautiful brother," musician Patti Smith wrote in a comment on Rain's post. "And blessings on all the Phoenix’s. 💙"
The eldest of the five Phoenix siblings, River was born in Madras, Oregon, and traveled internationally with his family as missionaries for the religious movement the Children of God.
While living in Venezuela, he and Rain formed a singing duet to help their family make ends meet; the actor told PEOPLE back in 1986 that they would sometimes perform “at airports and in front of hotels — ya know, to eat.”
The Phoenix family parted ways with the Children of God and returned to the United States in 1977, eventually settling in California. River gained his first acting jobs in commercials along the way and gained his first major role in the 1982-83 television series Seven Brides for Seven Brothers.
He later made his feature-film debut in 1985’s Explorers alongside another newcomer at the time, Ethan Hawke.
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Phoenix found his breakout role in 1986's Stand By Me, the Rob Reiner-directed film adapted from Stephen King's 1982 novella The Body. Phoenix played one of four friends who set out to find the body of a local missing boy in the Academy Award-nominated film.
Two years later, River received his own Oscar nod for his role as Danny Pope in 1988’s Running on Empty. The young actor continued to make a name for himself in Hollywood with an appearance as a young Indiana Jones in 1989’s box-office hit Indiana Jones and the Last Crusade, and as Carl in 1992’s star-studded feature Sneakers.
River found passions in activism — he was a vegetarian from age 8 onward — and music in addition to his acting career. He and Rain formed and performed in a band called Aleka’s Attic, and River befriended young musicians and actors in Los Angeles like Keanu Reeves.
The actor died in the early morning of Halloween 1993 outside the Los Angeles venue The Viper Room, after he collapsed on the sidewalk.
River's girlfriend at the time, Samantha Mathis, and younger brother Joaquin Phoenix were among those present at the time of his death; Leonardo DiCaprio has also said he briefly encountered River at a separate event the night he died.
“I knew something was wrong that night, something I didn’t understand," Mathis, now 53, told The Guardian of River's death back in 2018. "I didn’t see anyone doing drugs but he was high in a way that made me feel uncomfortable — I was in way over my head.”
“Forty-five minutes later, he was dead,” the Super Mario Bros. actress said at the time.
Last year, River's mother Arlyn "Heart" Phoenix celebrated his life on his 52nd birthday when she shared a throwback black-and-white photo of the duo on Instagram alongside a caption that read, "On August 23, 1970, at 12:03 PM in a little town called Madras in Oregon, I became a mother."
"52 years ago I experienced a LOVE beyond all of my understanding which transformed my life and multiplied in and out of my being," continued Heart, 78. "During the past years since I have posted on Facebook, I have shared how deeply his life and passing affected me. He remains a guiding light on my pathway forward."
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