rectus femoris
The hip flexor muscle is located in the front of the hip and upper thigh area in the human body.
The only knee flexor that originates superior to the acetablulum is the sartorius muscle
sartorius
The strongest Flexor of the hip (thigh) is illiopsoas muscle which is the merger of the illiacus and the psoas major muscle. The illiacus is on the medial side of the pelvic bone attaching to the femur and the psoas major muscle attaches from the lumbar vertebrae to the femur.
The quadriceps perform knee extension, however, the rectus femoris, which is one of the 4 muscles of the quadriceps, also does hip flexion.
The Gastrocnemius. There is another muscle involved in plantar flexion. The soleus and the tibialus posterior maintains the arch. The only one that does both actions, though, is the Gastrocnemius.
The Rectus Femoris
The strongest Flexor of the hip (thigh) is illiopsoas muscle which is the merger of the illiacus and the psoas major muscle. The illiacus is on the medial side of the pelvic bone attaching to the femur and the psoas major muscle attaches from the lumbar vertebrae to the femur.
The quadriceps muscle helps straighten and extend the leg and the hamstring helps bend the knee.
The flexor would be the hamstring, and gastrocnemius, which bend/flex the knee. The quadriceps, are extensors, which straighten/extend the knee.
Your hip flexor hurts
Hip flexor is a common name for the quadriceps, the large thigh muscles involved in both straightening the knee and bending the hip.