A unit load lifter mountable on an autonomous mobile robot to carry a unit load, comprising: a horizontal slide unit, comprising: a base plate of the unit load lifter mountable on the AMR, wherein the base plate is configured to hold a plurality of components of the unit load lifter; a plurality of unit load resting surfaces (402A-D) mounted on to the base plate with a plurality of stand-offs (404A-B), wherein the unit load is mountable on at least two unit load resting surfaces from the plurality of unit load resting surfaces (402A-D); a plurality of fixed guides (120A-N) integrated with the base plate that house a vertical axis fork assembly by a plurality of rollers (218A-N), wherein the plurality of rollers (218A-N) are mounted on a roller mounting plate; a pinion gear and a motor mounted on the vertical axis fork assembly coupled with a rack gear for creating a desired horizontal motion; and a plurality of counterbalance curvy slides (302A-B) integrated with the base plate; and wherein the vertical axis fork assembly comprises: a support plate weldment with the plurality of rollers (218A-N) integrated on either side to roll on at least one channel in the plurality of fixed guides (120A-N) of the horizontal slide unit to create a horizontal motion of the vertical axis fork assembly; a plurality of linear motion guide blocks (206A-N) sandwiched between a sliding plate and a plurality of linear motion rails (228A-N), wherein the sliding plate is configured to slide vertically and linearly up and down, wherein the plurality of LM rails (228A-N) are mounted on a vertical mounting plate; at least one fork from a plurality of forks (208A-B) is vertically mounted on the sliding plate; and an actuating end of a linear actuator connected to the sliding plate to drive the at least one fork up and down. a base plate of the unit load lifter mountable on the AMR, wherein the base plate is configured to hold a plurality of components of the unit load lifter; a plurality of unit load resting surfaces (402A-D) mounted on to the base plate with a plurality of stand-offs (404A-B), wherein the unit load is mountable on at least two unit load resting surfaces from the plurality of unit load resting surfaces (402A-D); a plurality of fixed guides (120A-N) integrated with the base plate that house a vertical axis fork assembly by a plurality of rollers (218A-N), wherein the plurality of rollers (218A-N) are mounted on a roller mounting plate; a pinion gear and a motor mounted on the vertical axis fork assembly coupled with a rack gear for creating a desired horizontal motion; and a plurality of counterbalance curvy slides (302A-B) integrated with the base plate; and wherein the vertical axis fork assembly comprises: a support plate weldment with the plurality of rollers (218A-N) integrated on either side to roll on at least one channel in the plurality of fixed guides (120A-N) of the horizontal slide unit to create a horizontal motion of the vertical axis fork assembly; a plurality of linear motion guide blocks (206A-N) sandwiched between a sliding plate and a plurality of linear motion rails (228A-N), wherein the sliding plate is configured to slide vertically and linearly up and down, wherein the plurality of LM rails (228A-N) are mounted on a vertical mounting plate; at least one fork from a plurality of forks (208A-B) is vertically mounted on the sliding plate; and an actuating end of a linear actuator connected to the sliding plate to drive the at least one fork up and down. a support plate weldment with the plurality of rollers (218A-N) integrated on either side to roll on at least one channel in the plurality of fixed guides (120A-N) of the horizontal slide unit to create a horizontal motion of the vertical axis fork assembly; a plurality of linear motion guide blocks (206A-N) sandwiched between a sliding plate and a plurality of linear motion rails (228A-N), wherein the sliding plate is configured to slide vertically and linearly up and down, wherein the plurality of LM rails (228A-N) are mounted on a vertical mounting plate; at least one fork from a plurality of forks (208A-B) is vertically mounted on the sliding plate; and an actuating end of a linear actuator connected to the sliding plate to drive the at least one fork up and down.