(written from a Production point of view)
Gary Gero (born 1946) is an animal handler and trainer who worked with his company Birds & Animals Unlimited on Star Trek: The Next Generation and Star Trek: Deep Space Nine. He trained and handled Monster for the fourth season episode "In Theory" in 1991 and twelve guinea fowls for the fifth season episode "Ensign Ro". Gero and his company are probably best known for the animal supervision and as owl trainer on the Harry Potter films Harry Potter and the Sorcerer's Stone (2001), Harry Potter and the Chamber of Secrets (2002), Harry Potter and the Prisoner of Azkaban (2004), Harry Potter and the Goblet of Fire (2005), Harry Potter and the Order of the Phoenix (2007), and Harry Potter and the Half-Blood Prince (2009).  
Gero was raised on a ranch in Northern California and started to work with falcons at early age. He was soon hired by an animal trainer and worked for him for several years before he started his own business.
Throughout his career, which spanned over 30 years in the business, Gero trained birds, hawks, wolves, bugs, dogs, cows, and orangutans for films such as the science fiction adventure Glen and Randa (1971), the adventure Mountain Family Robinson (1979), the drama Never Cry Wolf (1983), the war drama Birdy (1984), the drama Ladyhawke (1985), the romance Pretty in Pink (1986), John Carpenter's horror thriller Prince of Darkness (1987), the science fiction sequel Back to the Future Part II (1989, starring Christopher Lloyd), the television series Dark Shadows (1991, starring Jean Simmons and Ben Cross), the action sequel Lethal Weapon 3 (1992), the comic adaptation Batman Returns (1992), the fantasy film Death Becomes Her (1992), the fantasy film The Crow (1994), the adventure The Jungle Book (1994), the family movie 101 Dalmatians (1996) and its sequel 102 Dalmatians (2000), the comedy Doctor Doolittle (1998), Joe Dante's Small Soldiers (1998, with Kirsten Dunst), the comic adaptation Inspector Gadget (1999), the action film Casino Royale (2006), and the comic adaptation Thor (2011, starring Chris Hemsworth).