News Robert Downey Jr. Reveals His 5 Favorite Instagram Accounts -- Including 'Science Bro' Mark Ruffalo! By Leanne Aguilera 4:35 PM PDT, October 6, 2015 Instagram Happy Birthday, Instagram!To celebrate the fact that the social media platform is officially five-years-old, some of the biggest insta-celebs are naming their favorite accounts to follow.ETonline is exclusively revealing the five top Instagram accounts that Marvel mega-actor, Robert Downey Jr., loves to double tap the most. PHOTOS: Britney Spears Crashes Kate Hudson's Game Night1. Beth Stern (@Bethostern)RDJ's Reasoning: "Sterns and cats." View this post on InstagramMy new children's book, YODA GETS A BUDDY is on Amazon now for pre-order! Will be released December 1st. Perfect holiday gift and 100% of my proceeds go to @animalleague You buy a book and you help save more lives... Xoxo #howardandbuddyA post shared by Beth Stern (@bethostern) on Sep 27, 2015 at 5:15am PDT2. Bow & Arrow (@BowandArrow78)RDJ's Reasoning: "I’m a sucker for Bruce Lee merch." 3. Banksy (@BanksyNY)RDJ's Reasoning: "Iconoclast." MORE: Kourtney Kardashian Reacts to Scott Disick's 18-Year-Old Girlfriend4. Mark Ruffalo (@markruffalo)RDJ's Reasoning: "#ScienceBros." 5. Robert Downey, Jr.(@robertdowneyjr)RDJ's Reasoning: "Gotta love yourself." View this post on InstagramHappy birthday, America! Now let’s blow the roof off this joint. (Disclaimer: please practice safe fireworking.)A post shared by Robert Downey Jr. (@robertdowneyjr) on Jul 4, 2015 at 9:00am PDTWhat are your favorite accounts to follow on Instagram? Share your thoughts with @ETnow on Twitter!Is Kylie Jenner wearing buttpads in this Instagram photo? See her response in this video below!Is Kylie Jenner Wearing Butt Pads? See The Pic -- And Her Response!