It's tricky to definitively say which horse is the *biggest* in the world, as size can be measured by height, weight, or other factors, and records aren't always perfect.
However, the title of "tallest horse ever" often goes to "Big Jake," a Belgian gelding who stood 6 feet 4 inches (1.93 meters) tall at the shoulder. He passed away in 2010.
As for weight, "Big Jake" weighed a massive 2,860 pounds (1,297 kg). While record-breaking, other horses have also been very large.
Important note: These are notable examples, but other horses may have been just as big without well-documented records.