(Portland, OR) -- One of the oldest and largest and most beloved bull elephants in North America is being mourned after it died on Monday at the Oregon Zoo. Tusko was put to sleep after animal care could no longer help with mobility issues that were from a decades-old foot injury. The 45-year-old elephant had developed severe swelling and limited motion in his foot this week. At one point, the animal was using its trunk to help support his weight. Tusko leaves behind two offspring and four other elephants at the Oregon Zoo.