Answer by taking a quote from the following article:

Born in Riverside, California to Patricia (nee Howard) and former major leaguer Bobby Bonds, Bonds grew up in San Carlos and attended Junipero Serra High School in San Mateo, where he excelled in baseball, basketball, and football. He played on the junior varsity team during his freshman year and the remainder of his high school career on the varsity team. He garnered a .467 batting average his senior year, and was named prep All-American. The Giants drafted Bonds in the second round of the 1982 MLB draft as a high school senior, but the Giants and Bonds were unable to agree on contract terms when Tom Haller's maximum offer was $70,000 ($177,510 today) and Bond's minimum to go pro was $75,000, so Bonds instead decided to attend college.

Since 2003, Bonds has been a key figure in the Bay Area Laboratory Co-operative (BALCO) scandal. BALCO marketed tetrahydrogestrinone ("the Clear"), a performance-enhancing anabolic steroid that was undetectable by doping tests. He was under investigation by a federal grand jury regarding his testimony in the BALCO case, and was indicted on perjury and obstruction of justice charges on November 15, 2007. The indictment alleges that Bonds lied while under oath about his alleged use of steroids.  In 2003, Bonds first became embroiled in a scandal when Greg Anderson of the Bay Area Laboratory Co-operative (BALCO), Bonds's trainer since 2000, was indicted by a federal grand jury in the United States District Court for the Northern District of California and charged with supplying anabolic steroids to athletes, including a number of baseball players. This led to speculation that Bonds had used performance-enhancing drugs during a time when there was no mandatory testing in Major League Baseball. Bonds declared his innocence, attributing his changed physique and increased power to a strict regimen of bodybuilding, diet, and legitimate supplements.  During grand jury testimony on December 4, 2003, Bonds said that he used a clear substance and a cream that he received from his personal strength trainer, Greg Anderson, who told him they were the nutritional supplement flaxseed oil and a rubbing balm for arthritis. This testimony, as reported by Lance Williams and Mark Fainaru-Wada, has frequently been misrepresented. Later reports on Bonds's leaked grand-jury testimony contend that he admitted to unknowingly using "the cream" and "the clear".  In July 2005, all four defendants in the BALCO steroid scandal trial, including Anderson, struck deals with federal prosecutors that did not require them to reveal names of athletes who may have used banned drugs.

Who was the trainer?
Greg Anderson, who told him they were the nutritional supplement flaxseed oil and a rubbing balm for arthritis.