Gary Cooper

Context: In early 1925, Cooper began his film career in silent pictures such as The Thundering Herd and Wild Horse Mesa with Jack Holt, Riders of the Purple Sage and The Lucky Horseshoe with Tom Mix, and The Trail Rider with Buck Jones. He worked for several Poverty Row studios, including Famous Players-Lasky and Fox Film Corporation. While his skilled horsemanship led to steady work in Westerns, Cooper found the stunt work--which sometimes injured horses and riders--"tough and cruel". Hoping to move beyond the risky stunt work and obtain acting roles, Cooper paid for a screen test and hired casting director Nan Collins to work as his agent. Knowing that other actors were using the name "Frank Cooper", Collins suggested he change his first name to "Gary" after her hometown of Gary, Indiana. Cooper immediately liked the name.  Cooper also found work in a variety of non-Western films, appearing, for example, as a masked Cossack in The Eagle (1925), as a Roman guard in Ben-Hur (1925), and as a flood survivor in The Johnstown Flood (1926). Gradually, he began to land credited roles that offered him more screen time, in films such as Tricks (1925), in which he played the film's antagonist, and the short film Lightnin' Wins (1926). As a featured player, he began to attract the attention of major film studios. On June 1, 1926, Cooper signed a contract with Samuel Goldwyn Productions for fifty dollars a week.  Cooper's first important film role was in The Winning of Barbara Worth (1926) with Ronald Colman and Vilma Banky, in which he plays a young engineer who helps a rival suitor save the woman he loves and her town from an impending dam disaster. Cooper's experience living among the Montana cowboys gave his performance an "instinctive authenticity", according to biographer Jeffrey Meyers. The film was a major success. Critics singled out Cooper as a "dynamic new personality" and future star. Goldwyn rushed to offer Cooper a long-term contract, but he held out for a better deal--finally signing a five-year contract with Jesse L. Lasky at Paramount Pictures for $175 a week. In 1927, with help from Clara Bow, Cooper landed high-profile roles in Children of Divorce and Wings, the latter being the first film to win an Academy Award for Best Picture. That year, Cooper also appeared in his first starring roles in Arizona Bound and Nevada--both films directed by John Waters.  In 1928, Paramount paired Cooper with a youthful Fay Wray in The Legion of the Condemned and The First Kiss--advertising them as the studio's "glorious young lovers". Their on-screen chemistry failed to generate much excitement with audiences. With each new film, Cooper's acting skills improved and his popularity continued to grow, especially among female movie-goers. During this time, he was earning as much as $2,750 per film and receiving a thousand fan letters a week. Looking to exploit Cooper's growing audience appeal, the studio placed him opposite popular leading ladies such as Evelyn Brent in Beau Sabreur, Florence Vidor in Doomsday, and Esther Ralston in Half a Bride. That year, Cooper also made Lilac Time with Colleen Moore for First National Pictures, his first movie with synchronized music and sound effects. It became one of the most commercially successful films of 1928. CANNOTANSWER

Question: what was Gary Cooper's greatest achievement?
Answer: Lilac Time with Colleen Moore for First National Pictures, his first movie with synchronized music and sound effects. It became one of the most commercially successful films of 1928.